The Hydrologic History of the San Carlos Reservoir, Arizona, 1929-71, with Particular Reference to Evapotranspiration and Sedimentation
GEOLOGICAL SURVEY PROFESSIONAL PAPER 655-N
The Hydrologic History of the San Carlos Reservoir, Arizona, 1929-71, with Particular Reference to Evapotranspiration and Sedimentation
By FRANK P. KIPPLE
GILA RIVER PHREATOPHYTE PROJECT
GEOLOGICAL SURVEY PROFESSIONAL PAPER 65 5-N
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977 UNITED STATES DEPARTMENT OF THE INTERIOR
CECIL D. ANDRUS, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
Library of Congress Cataloging in Publication Data
Kipple, Frank P. The hydrologic history of the San Carlos Reservoir, Arizona, 1929-71, with particular reference to evapotranspiration and sedimentation.
(Gila River phreatophyte project) (Geological Survey Professional Paper 655-N) Bibliography: p. N40. 1. Hydrology~Arizona~San Carlos Reservoir. 2. Evapotranspiration-Arizona-San Carlos Reservoir. 3. Sediments (,geology)-Arizona-San Carlos Reservoir. I. Title: The hydrologic history of the San Carlos Reservoir... II. Series. III. Series: United States Geological Survey Professional Paper 655-N. QE75.P9 no. 655-N [GB705.A6] 557.3'03s [551.4'82'0979'54] 77-608085
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02976-6 CONTENTS
Page Pare Conversion factors ...... V Hydrology ...... Nl4 List of symbols ...... V Water-budget equation ...... 14 Abstract ...... Nl Surface flow ...... 15 Introduction ...... 1 Gila River and San Carlos River inflow ...... 15 Purpose and scope ...... 1 Tributary inflow ...... 16 Acknowledgments ...... 1 Gila River outflow ...... 18 History of the San Carlos Project ...... 2 Ground-water inflow ...... 18 Definitions ...... 2 Precipitation ...... 19 Reservoir sediment ...... 3 Evaporation ...... 19 Sediment deposition and capacity surveys ...... 3 Water stage and surface-water storage at San Carlos Surface-water storage losses from sediment Reservoir ...... 2.2 accumulation ...... 5 Bank storage ...... 24 Sediment distribution ...... 6 Water-budget analyses ...... 27 The effect of phreatophytes on inflow channels ...... 7 Evapotranspiration ...... 27 Sediment trap efficiency ...... 11 Development of surface-water storage-capacity ratings ...... 31 Analysis of sediment data ...... 13 Simulation of the sediment depositional process ...... 31 Interpolation of elevation-capacity ratings between Interpretation of simulation results ...... 37 capacity surveys ...... 14 Procedure to develop ratings ...... 37 Summary and conclusions ...... 3n References cited ...... 40
ILLUSTRATIONS
Pare FIGURE 1. Map showing reservoir boundary, location of gaging stations, and centerline of San Carlos Reservoir ...... N3 2-5. Graphs showing: 2. Area curves for San Carlos Reservoir ...... 4 3. Capacity curves for San Carlos Reservoir ...... 5 4. Vertical distribution of the volume of sediment deposition with 5-ft (1.5 m)-elevation intervals at San Carlos Reservoir for the periods 1928-47 and 1947-66 ...... 8 5. Bottom profiles of San Carlos Reservoir along principal longitudinal axis as determined by the five capacity surveys ...... ^^ 9 6-11. Photographs showing: 6. Aerial view looking downstream (west) on April 20, 1965, showing the sediment flats at the confluence of the Gila and San Carlos Rivers within the San Carlos Reservoir ...... 10 7. Aerial view looking upstream (north) on April 20, 1965, showing the San Carlos River on the left and the Gila on the right ...... ^ 10 8. Aerial view of channel conditions of the Gila River upstream from the San Carlos River in 1935 7 years after the completion of Coolidge Dam ...... 10 9. Aerial view of conditions of a part of the Gila River channel above the San Carlos River in June 1962 ...... 10 10. View looking downstream (south) on August 18, 1965, at the Gila River flood plain from a point 2 mi (3.2 km) upstream from the mouth of the San Carlos River ...... 11 11. Flood-plain conditions after the area was inundated by the reservoir pool ...... 11 12. Map showing extent of channel plugging in the Gila River on indicated dates ..._...... 12 13. Graph of profiles along the longitudinal axis of San Carlos Reservoir showing changes in bed elevations and slope within the reach of channel plugging ...... 13 14. Photograph showing view of the Gila River looking north from a point 2.6 mi(4.2 km) upstream from the mouth of the San Carlos River photographed in September 1964 ...... 13 15. Photograph showing downstream view on July 15, 1965, of a reach of the Gila River channel which had been plugged in 1964 ...... 13 16. Photograph showing aerial view of channel plugging in the Gila River on July 22, 1964 ...... 13
ill IV CONTENTS Page FIGURES 17-31. Graphs showing: 17. Relation between accumulated decrease in storage capacity and accumulated streamflow by capacity survey periods ...... N15 18. Annual combined Gila River and San Carlos River inflows to San Carlos Reservoir for water years 1929-71 ...... 15 19. Frequency of occurrence of water-year inflow volumes, 1929-71 ...... 16 20. Mean monthly flow as a percent of mean annual for the Gila and San Carlos Rivers ...... 17 21. Relations between measured rainfall and tributary runoff for summer seasons 1964-71 from 72.6 mi2 (188 km2) of area tributary to San Carlos Reservoir ...... 18 22. Evaporation at San Carlos Reservoir for water years 1931-71 ...... 20 23. Five-year moving averages of pan evaporation at San Carlos Reservoir and the mean of pan evapora tion at Mesa, Roosevelt Lake, and at Tucson for water years 1931-71 ...... 21 24. Double-mass diagram of cumulative pan evaporation for San Carlos Reservoir and mean of Mesa, Roosevelt Lake, and at Tucson for water years 1931-71 ...... 21 25. Beginning-of-month lake stage of San Carlos Reservoir for water years 1929-71 ...... 23 26. Number of days in which lake stage was within a particular elevation interval for water years 1929-71 .. 24 27. Percentage of time lake stage of San Carlos Reservoir equaled or exceeded a given elevation for water years 1929-71 ...... _...... 24 28. Percentage of time usable surface-water storage of San Carlos Reservoir equaled or exceeded a given volume for water years 1929-71 ...... 25 29. Relations of cumulative ASg to cumulative AS# and cumulative AS# to cumulative ASy for the periods January through April 1965 and December 1967 through May 1968 ...... 26 30. Relation between the computed change in bank-storage capacity and elevation at San Carlos Reservoir for water years 1931-47 and 1948-71 ...... 27 31. Elevation-capacity relation for usable surface-water storage, usable bank storage, and total usable storage in 1966, for San Carlos Reservoir ...... 29 32. Sketch showing relative magnitude of inflow and outflow water-budget components ...... 31 33-36. Graphs showing: 33. Annual evapotranspiration from exposed area of reservoir, computed by reservoir water budget ...... 32 34. Annual depth of evapotranspiration from the exposed surface of San Carlos Reservoir for water years 1931-71 ...... 33 35. Computed monthly evapotranspiration at San Carlos Reservoir for water years 1931-71 ...... 33 36. Mean monthly evapotranspiration depths computed for 10-year periods ...... 33 37. Sketch identifying terms used in simulation of suspended sediment distribution ...... 35 38. Sketch showing distribution of suspended sediment, Ss ., when distance, D^, was computed as greater than the distance from inflow point (A) to the dam ...... 36 39. Graph showing simulated sediment deposition, in percent, downstream from point of inflow ...... 37 40. Graphs showing comparison between the volumes of deposits measured and estimated for each incremental reservoir, 1929-66, and volumes of estimated and measured deposits cumulative by 5-ft-elevation increments upward from lowest part of reservoir, 1929-66 water years ...... 38
TABLES
Page TABLE 1. Results of surface-water storage-capacity surveys ...... N5 2. Storage capacities, sediment deposition, and streamflow data ...... 7 3. Volumes of sediment deposited by 5-ft-elevation intervals in San Carlos Reservoir during different periods...... 7 4. Maximum and minimum volumes of water supplied by streamflow into San Carlos Reservoir for different time durations ...... 16 5. Mean monthly inflows for the Gila River, the San Carlos River, and for both rivers, 1930-71 ...... 16 6. Tributary inflow into the San Carlos Reservoir along a reach of the Gila River ...... 17 7. Estimated tributary inflow into San Carlds Reservoir ...... 17 8. Mean monthly discharge of the Gila River below Coolidge Dam, 1931-71...... 18 9. Annual (water year) precipitation at San Carlos Reservoir, 1931-71 ...... 19 10. Mean monthly precipitation and monthly extremes (1931-71) at San Carlos Reservoir ...... 20 11. Evaporation at San Carlos Reservoir by water year, 1931-71 ...... 22 12. Mean monthly evaporation and mean monthly pan coefficients for San Carlos Reservoir ...... 23 13. Percent of time that available monthly surface-water storage was less than amount shown ...... 25 14. Example of water budget used to determine change in bank storage ...... !...... 25 15. Results of procedures to determine bank storage capacity at San Carlos Reservoir ...... 28 16. San Carlos Reservoir elevation-capacity tables of usable bank storage, usable surface-water storage, and total usable storage ...... 29 CONTENTS v
TABLE 17. Summations of San Carlos Reservoir inflow-outflow components by water year, 1931-71 ...... N30 18. Water-budget summations ...... 32 19. Total evapotranspiration for San Carlos Reservoir, by water year ...... 33 20. Mean monthly evapotranspiration computed from 4 periods of 10 years each, and median monthly evapotranspiration for 41 years...... 34 21. Chart of notation used to identify time and inflow location of computed proportional sediment weights, Sy^ ...... 34 22. Optimum values of variables from simulation of the sediment depositional procedure ...... '...... 36 23. Volumes of sediment deposits measured (Sjjffe) and computed (Sep for 1937-47, and the SMk/Sek ratios ...... 38 24. Estimated change in surface-water storage capacity, Z, from start of period 3 to 1942, by 5-ft-elevation increments .... 39 25. Computed capacity ratings of surface-water storage used for 1938 through 1942 ...... 39 26. Comparison of segments of surface-water storage capacity ratings made by curve fitting and by computer ...... 39
CONVERSION FACTORS
English Multiply by Metric (SI) acre-feet (acre-ft) 1.233 > 10-3 cubic hectometers (hm3) miles (mi) 1.609 kilometers (km) feet (ft) .3048 meters (m) cubic feet per second (ftVs) 2.832 10- 2 cubic meters per second (mVs) acres 4.047 10-3 square kilometers (km2) pounds per cubic feet (Ib/ft3) 16 kilograms per cubic meter (kg/m3) acre-feet per square mile (acre-ft/mi2) 0.476 cubic hectometers per square kilometer (hmVkni2) gallons per day per square foot [(gal/day)/ft2] 4.074 io-2 cubic meters per day per square meter [(m3/day)/rr2] inches (in.) 25.4 millimeters (mm) parts per million (ppm) l.OO1 milligrams per liter (mg/1)
LIST OF SYMBOLS
Gila River inflow at Calva Weight of sediment trapped by reservoir is San Carlos River inflow at Peridot E Sediment trap efficiency of a reservoir IT Tributary inflow into the San Carlos Reservoir Mean winter sediment concentration OG Gila River outflow below Coolidge Dam Mean summer sediment concentration IGW Ground-water inflow Winter streamflow summations IP Precipitation input over the lake surface Summer streamflow summations OE Evaporation from the lake surface Ratio of summer to winter concentrations Computed value proportional to weight of sediment °ET Evapotranspiration from the exposed surface of the deposited in a reservoir reservoir Incremental storage reservoir Change in surface-water storage Water year Change in bank storage The ratio of the weight of larger sediment particles Q Ground-water flow to the weight of total sediment K Hydraulic conductivity Distance estimated by simulation procedure from m Thickness of aquifer location of river discharge into the reservoir pool u Ground-water slope to the point where deposition is complete w Aquifer width Distance from any point along DA to point where P Rainfall distribution of sediment is complete Q Stream discharge Exponent of suspended sediment distribution Change in total reservoir storage SB Computed amount proportional to weight of sediment Weight of sediment discharge deposited between point of inflow and any other Mean sediment concentration downstream point
1 See "Water Resources Data for Arizona, Part 2, Water Quality Records, 1973" for conversion factors when sediment concentration exceeds 8,000 ppm (factor varies depending on specific gravity of sediment and density of water). VI CONTENTS
DA Estimated distance from location of river discharge Sdk,j A computed quantity which is proportioral to the into incremental reservoir i to the point where suspended sediment weight deposited in reservoir k deposition is complete during water year ; Incremental reservoir of deposition A computed quantity which is proportioral to the Distance from upstream point of incremental reser sediment weight deposited in an incremental reser voir k, in which simulated deposition is occurring, voir during a period to the point where deposition is complete The sum of all SR A computed quantity which is proportional to total The volume of sediment measured sediment weight entering an incremental reservoir SM from the stream RATIO A proportionality constant between sediirent mea A computed quantity which is proportional to weight sured and sediment estimated of suspended sediment inflow Estimate of the absolute sediment volume for incre A computed quantity which is proportional to weight mental reservoir k of suspended sediment deposited in reservoir k ZkJ The estimated decrease in storage for an incremental reservoir k from the start of a period to water year ; GILA RIVER PHREATOPHYTE PROJECT
THE HYDROLOGIC HISTORY OF THE SAN CARLOS RESERVOIR, ARIZONA, 1929-71, WITH PARTICULAR REFERENCE TO EVAPOTRANSPIRATION AND SEDIMENTATION
By FRANK P. KIPPLE
ABSTRACT An investigation of these changes, and of the Reservoir data records were used in an investigation of evapo- reservoir hydrology in general, was made to evaluate transpiration from the land area of San Carlos Reservoir and reservoir evapotranspiration (ET) and the change in evaporation from the water-surface area. A water-budget analysis ETfrom 1929 to 1971. The investigation was made as indicates that the evapotranspiration loss was 11.3 percent and part of the Gila River Phreatophyte Project, a study the evaporation loss was 10.5 percent of the total outflow from the reservoir during 1931-71. of the hydrologic effect of phreatophyte control by The water-budget computations were used to develop ratings the U.S. Geological Survey (Culler and others, 1970). relating lake stage to usable bank storage. The rating developed The evaluation of ET is made by use of a water- for the 1948-71 period indicates that usable bank storage is budget equation in which ETis the residual in the approximately 159,000 acre-ft (196 hm3), or about 14 percent of equation. total usable storage capacity, if the reservoir is filled to the spillway level of 2,511 ft (765 m). Secondary objectives included investigations of A procedure was developed to simulate sediment deposition in reservoir sediment deposition, lake evaporation, and the reservoir. The procedure was used to estimate the change in reservoir bank storage. These investigations were storage capacity between five reservoir capacity surveys made essential prior to compilation of the water budget. during the period 1914-66. Data sources for this report include five surveys of INTRODUCTION reservoir capacity which provide a history of capac PURPOSE AND SCOPE ity change and sediment accumulation. Investiga tions of tributary runoff, precipitation, evapotran Once a reservoir is put into operation, a number of spiration, and lake evaporation were made as part of progressive changes are produced which affect the the Gila River Phreatophyte Project and furnish hydrology of the reservoir. Prior to inundation, water information for this report. Other sources of data are vaporization from the reservoir area is from plant U.S. Geological Survey surface-water records (issued transpiration and from soils and off-channel pond annually), Gila River Water Commissioner reports ing. During inundation vaporization is evaporation (issued annually), log books of precipitation andp^n from the ponded water surface. The soils and topo evaporation at Coolidge Dam, and climatic data graphy are changed by the deposition of sediment published by the National Weather Service (issued and sometimes by bank erosion. The water table annually). adjacent to the reservoir rises, and the bank storage of water is increased. Vegetation on exposed parts of ACKNOWLEDGMENTS the reservoir may be altered because of changes in Much of the planning and data interpretation for soils and water availability. These changes are this report was contributed by R. C. Culler, project particularly significant for reservoirs where the chief of the Gila River Phreatophyte Project. Preprr- streams convey large quantities of sediment and ation of the report was under the direction of R. L. where fluctuations of the reservoir water level and Hanson. Assistance and cooperation were received the water surface areas are large. The records of from personnel of the Arizona District office, U.S. inflow, outflow, surface-water storage, and sediment Geological Survey, and of the San Carlos Project of deposition provide the data for evaluating some of the U.S. Bureau of Indian Affairs, supervised by 1 1. the changes for the San Carlos Reservoir. D. Young, general engineer. Computations of lake
Nl N2 GILA RIVER PHREATOPHYTE PROJECT evaporation by energy-budget and mass-transfer water for irrigation of 100,000 acres (405km2) of land methods were principally by J. Stuart Meyers, U.S. within the San Carlos Project. Fifty thousand acres Geological Survey. (202 km2) are Indian lands within the Gila River HISTORY OF THE SAN CARLOS PROJECT Reservation, and 50,000 acres (202 km2) are privately owned lands in the Florence-Casa Grande Valley. The San Carlos Project was established to provide Water released from Coolidge Dam is diverted from irrigation water to the Middle Gila District, Gila the Gila River channel at the Ashurst-Hayder Diver River Basin, Ariz. The district was defined by Davis sion Dam 68 mi (109 km) downstream. A power plant (1897, p. 17) as "that portion from the mouth of Salt at Coolidge Dam contains two generators having a River to The Buttes above Florence and including the combined output of 10,000 kilo volt-amperes. Power Pima Indian Reservation and the great Casa Grande generation is subordinate to irrigation requir?ments Valley." Diversions of water from the upstream and is stopped when irrigation demands are cur reaches of the Gila River by farmers during the tailed. The reservoir is also used for recreation, and period 1870-86 imperiled the water rights of the the recreational facilities are operated under lease by Indians on the Pima Reservation. An investigation the San Carlos Apache Indian Tribe. Flood protec was made by the Geological Survey to examine the tion provided by the reservoir is an incidental possibility of providing a firm water supply to the benefit. Indians as reported by Davis (1897, p.-71). The construction of a dam on the Gila River at The Buttes Water in the Gilla River was adjudicated by a court 14 mi (23 km) east of Florence was recommended. decree entered in 1935 (U.S. vs. Gila Valley Irrig. Numerous other feasibility studies were made during Dist. et al., 1935). Briefly, the decree divides the the next 15 years, culminating in a report by the U.S. water between the upstream users in the Safford and Army Corps of Engineers (1914) recommending a Duncan Valleys, the Gila Valley Irrigation District, dam on the Gila River. and the downstream users of the San Carlos Irriga On June 7, 1924, Congress approved legislation tion Project, on the basis of priority of appropriation. that authorized the Secretary of the Interior through In addition to priority rights, upstream users are also the Indian Service to construct a dam at the San entitled to apportioned rights, which are dependent Carlos site as part of the San Carlos Project. The on the amount of water stored in San Carlos Reser construction of Coolidge Dam was started in Janu voir. As defined in the decree, the rights are deter ary 1927 and completed in October 1928. Water im mined as follows: On January 1 of each yeer, or as poundment began on November 15, 1928. The area soon thereafter as there is water stored in the San within the boundary of the reservoir is administered, Carlos Reservoir, which is available for release for and the facilities at Coolidge Dam are operated, by use on lands of the San Carlos Project, the Gila Water the San Carlos Project, an agency of the Bureau of Commissioner, who is appointed by the court to Indian Affairs. enforce the decree, shall apportion for the ensuing Coolidge Dam is located in sec. 17, T. 3 S., R. 18 E., irrigation year to irrigated lands above the San Gila County, Ariz., in the San Carlos Indian Reser Carlos Reservoir from the natural flow of the Gila vation (fig. 1). The dam is a multidomed structure River an amount of water equal to that stored in the having a length, including two spillways, of 850 ft San Carlos Reservoir less losses. It is also provided (259 m). Each of the three domes has a span of 180 ft that if and when at any time, or from time to time, (55 m) and a base thickness of 28 ft (8.5 m). The thick during the year storage in the reservoir shall be ness decreases to 4 ft (1.2 m) at the top. The dam rises increased and made available to downstream users, 203 ft (62 m) to the spillway at elevation 2,511 ft (765 the Commissioner shall make further and additional m) above mean sea level and approximately an addi apportionments to upstream users which fhall be tional 25 ft (7.6 m) to the highway on top of the dam. equivalent in amount to the newly available stored A spillway is located on each side of the dam. Each water supply. spillway has three gates 50 ft (15 m) wide and 12 ft DEFINITIONS (3.7 m) high. Maximum storage capacity of 1,267,000 The following are definitions of terms as used acre-ft (1,560 km3) at elevation 2,523 ft (769 m) is throughout this report: reached when the gates are raised. The gates are now inoperative in the lowered position. The maximum Water year...... ~October 1 to September 30 safe release from spillways and outlets is 122,000 Surface-water storage The above-ground volume of a reservoir ftVs (3,455 mVs). The sill of the lowest outlet gate is capacity available to store water Dead storage capacity, The above-ground volume of a reservoir at elevation 2,382.63 ft (726 m), providing an oper surface water below the invert of the lowest reser ating range, outlet to spillway, of 128.37 ft (39.13 m). voir outlet, which cannot be evacuated The principal purpose of the reservoir is to store by gravity HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 I T3
110
AREA 32 ^- Tucson INDEX MAP 0 50 100MILES
0 50 100 Kl LOMETERS
\
110 30' Base from U.S. Geological Survey 2345 KILOMETERS Mesa 1:250,000, 1954
CONTOUR INTERVAL 200 FEET WITH SUPPLEMENTARY CONTOURS AT 100-FOOT INTERVALS DATUM IS MEAN SEA LEVEL
FIGURE 1. Map showing reservoir boundary, location of gaging stations, and centerline of San Carlos Reservoir.
Usable surface-water The difference between surface-water reservoir and the volume of sediment which passes storage capacity storage capacity and dead storage ca through the reservoir by (1) regulating the stage, rate pacity, defined as the volume available for release below the stage of maxi of water release, and frequency of sediment wetting mum controllable level and drying, (2) vegetative clearing, and (3) channel Usable bank-storage The below-ground volume in the banks of dredging. An inventory of sediment deposition can capacity a reservoir available for storage which be obtained by use of data from reservoir-capacity can be evacuated by gravity surveys. In addition, these surveys provide the data used to establish the elevation-capacity and eleva RESERVOIR SEDIMENT tion-area ratings, which are needed for water SEDIMENT DEPOSITION AND CAPACITY SURVEYS management. Sediment deposition in a reservoir, and the result The volume of sediment deposited in the £ pleted in 1935 and 1937 by the Soil Conservation of 51 range lines were established near the water's Service, the third at the request of the Gila Water edge, and a recording fathometer was used to obtain Commissioner. A fourth survey was made in 1947 by a continuous record of the ground profile along each the Corps of Engineers to assess changes in the range line. The shorelines shown on aerial photog capacity of the reservoir, mainly resulting from raphy taken during 1966-67 were used to check above-normal inflow in 1941-42 (Thorp and Brown, some of the topographic data. Topographic changes 1951). A map of the reservoir, scale 1:7,200, was within the study area of the Gila River PhreatcT>hyte produced by photogrammetric methods from the Project above the maximum 1966 pool leve? were 1947 survey. Changes during the period 1947-66 obtained from cross-valley profiles repetitively sur were assessed by a fifth survey made in 1966 by the veyed (Burkham, 1972). Elevation data were plotted U.S. Geological Survey. on copies of 1947 reservoir topographic maps of the The survey of 1966 was made primarily to provide U.S. Army Corps of Engineers and were used to better water-surface area and storage-capacity data locate 5-ft (1.5 m) contours for 1966. for the water-budget analysis of evapotranspiration. Area curves from the five capacity surveys are con An above-normal lake level during the summer of tained in figure 2. Reservoir capacities between con 1966 provided an opportunity to obtain an economi secutive 5-ft (1.5 m) contours were computed using cal survey of the reservoir. Control points at-theends the elevation-area data of each survey. The curves of WATER-SURFACE AREA, IN THOUSANDS OF SQUARE HECTOMETERS 1 234567 2530 - 770 Top of fully raised gates, 2, 523 ft 2520 Top of spillway crest, 2, 511 ft 2510 765 2500 - 760 -1 -" 2480 755 LU LU W _* 2470 Z LU ^ 2460 LU O 2450 DO -745 I- 2440 LU LU LL z 2430 - 740 O 2420 H > 2410 - 735 LU ^ 2400 730 2390 Elevation at top of dead storage pool, 2, 382.63 ft 2380 - 725 2370 I I I | I I - 720 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 WATER-SURFACE AREA, IN THOUSANDS OF ACRES FIGURE 2. Area curves for San Carlos Reservoir. HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N5 figure 3 show the elevation-capacity relations for all duced some of the increases, however, the increases surveys. Water-surface areas and surface-water extend about 25 ft (7.6 m) above the maximum water storage capacities for the surveys are listed by 5-ft stage recorded prior to the 1937 surveys. The maxi (1.5 m)-elevation increments in table 1. Much of table mum reservoir elevation through 1937 was 2,471.56 ft 1 data is from Thorp and Brown (1951, table 1). (753 m), April 5, 1932. Another example of error in The earlier capacity surveys were not as detailed the first two surveys is indicated by no measured as later surveys because the needs were different. capacity change between surveys above certain The 1914-15 reservoir survey was designed to de stages, although considerable inflow occurred when scribe agricultural lands and land use on the Gila the reservoir water level exceeded those stages. TNe and San Carlos River flood plains. The topography 1935 capacity table was identical to the 1914-15 table outside the flood plain area was included in this above 2,435 ft (742 m) elevation, yet about 668,010 survey but was with less detail. More attention was acre-ft (824 hm3) of inflow occurred above this given to defining flood-plain topography in the 1935 elevation during 1928-35. and 1937 surveys. Not until the 1947 survey, how ever, was the upland topography well defined. Ca SURFACE-WATER STORAGE LOSSES FROM pacity ratings for the first three surveys were ad SEDIMENT ACCUMULATION justed to the more accurate 1947 survey by Thorp and The maximum surface-water storage capacity of Brown (1951, p. 9, 10) and are shown in table 1. The the San Carlos Reservoir in November 1928 w*s errors remaining after adjustments are significant 1,266,837 acre-ft (1,562 hm3) at 2,523 ft (769 m). Py in the analyses of this report. As an example of the 1966, sediment deposition had reduced the capacity errors remaining in the ratings, it is seen in table 1 by 96,719 acre-ft (119 hm3) to 1,170,118 acre-ft (1,443 that capacities computed for 5-ft-elevation incre hm3), a 7.6 percent loss. The loss in usable surface- ments in 1937 were greater than for corresponding 5- water storage capacity was 72,476 acre-ft (89 hm3) for ft increments in 1935, in the range of 2,435 to 2,495 ft the same period. (742-760 m). Scour or compaction might have pro These storage losses indicating that the total CAPACITY, IN CUBIC HECTOMETERS 500 600 700 800 900 1000 1100 2530 Elevation of maximum capacity, 2, 523 ft Spillway crest, 2, 511 ft -- -.. ^^-'^^-^ EXPLANATION Elevation at top of dead storage pool, 2, 382.63 ft 720 2360 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 CAPACITY, IN THOUSANDS OF ACRE-FEET FIGURE 3. Capacity curves for San Carlos Reservoir. N6 GILA RIVER PHREATOPHYTE PROJECT TABLE 1. Results of surface-water storage-capacity surveys 1914-15 survey (adjusted)1 1935 survey (adjusted) 1937 survey (adjusted) 1947 survey 1966 survey Elevation Capacity Capacity Capacity Capacity Capacity above to next to next to next to next to next mean sea lower Cumulative lower Cumulative lower Cumulative lower Cumulative lower Cumulative level Area contour capacity Area contour capacity Area contour capacity Area contour capacity Area contour capacity (ft) (acres) (acre-ft) (acre-ft) (acres) (acre-ft) (acre-ft) (acres) (acre-ft) (acre-ft) (acres) (acre-ft) (acre-ft) (acres) (acre-ft) (acre-ft) 2308 ...... Orignal b volume of sediment deposited was 96,719 acre-ft (119 with respect to the flood plain at a distance of 42,000 hm3) also indicate that the mean annual volume for to 58,000 ft (12,800 to 17,700 m) upstream f-om the the period November 1928 to August 1966 was 2,553 dam. The centerline, as revised, is shown in figure 1. acre-ft (3.1 hm3), which is equivalent to 0.20 percent Centerline distances from the dam to intercepts of of the original surface-water storage capacity. Table centerline and contour lines were scaled from maps 2 includes storage capacity data, sediment deposi of all surveys except the 1937 survey, for which no tion amounts and mean rates of deposition, and a maps were available. Centerline distances for the comparison of sediment volume deposited to stream- 1937 survey were based on the 1937 capacity-survey flow volume for all periods between surveys. data and the 1935 centerline distances. Longitudinal slope of the reservoir bottom below SEDIMENT DISTRIBUTION the 2,380-ft (725 m) contour has decreased from The data of table 1 were used to calculate the 0.00246 to 0.00057 during 1929-66. Above the 2,380-ft volumes of sediment deposition for 5-ft (1.5 m)-eleva- (725 m) contour the slope has decreased from 0.00167 tion increments for the periods 1928-47,1947-66, and to 0.00138. Over the entire 22-mi (35.4 km) reservoir 1928-66. (The capacity tables used in 1928 were length, the mean slope was 0.00188 in 1928, 0.00140 obtained from the 1914-15 survey.) The computed in 1935 and 1937, 0.00135 in 1947, and 0.00131 in volumes are given in table 3 and are illustrated in the 1966. The longitudinal slope of the San Carlo,*? arm of vertical distribution graph of figure 4. Changes in the reservoir is about 0.00275. Changes in slope due elevation along the centerline of the reservoir result to channel plugging are discussed in th«* next ing from sediment deposition are evident from the section. profiles shown in figure 5 for all surveys. The A large sediment accumulation occurred in the longitudinal centerline, as established on maps of lower parts of the reservoir, as indicated in table 3 the 1947 survey, was changed to more nearly center it and figures 4 and 5, which corresponds to the most HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 ! T7 TABLE 2. Storage capacities, sediment deposition, and streamflow data A. Storage capacities Year of survey 1928' 1935 1937 1947 1966 Surface-water storage capacity in acre-ft, at 2,523 ft (gates fully raised) ...... 1,266,837 1,232,725 1,230,695 1,209,343 1,170,118 Surface-water storage capacity in acre-ft, at 2,511 ft (spillway crest) ...... 1,046,203 1,012,091 1,010,061 988,709 949,484 Usable surface-water storage capacity in acre-ft, at 2,511ft ...... 1,021,060 1,000,916 999,231 984,875 948,584 Dead storage capacity in acre-ft, at 2,382.63 ft ...... 25,143 11,175 10,830 3,834 900 Elevation of zero surface storage at time of capacity survey, in feet ...... 2,309 2 2,354 2 2,354 2,370 2,374 B. Sediment deposition Period 1928-351 1935-37 1937-47 1947-66 1928-661 6.28 1.91 10.00 19.70 37.89 04 119 2,030 21,352 39,225 96,719 5,431 1,063 2,135 1,991 2,553 Sediment deposition per period in percent of original surface-water storage capacity at 2,523 ft ...... 2.69 .16 1.69 3.09 7.63 Mean annual sediment deposited per period as percent of original surface-water .43 .08 .17 .16 .20 13,968 345 6,996 2,934 24,243 Dead storage loss by sediment deposition per period, in percent of original dead storage 55.55 1.37 27.83 11.67 96.42 . .. 1,722,985 345,275 2,541,463 3,579,217 8,188,940 .0198 .0059 .0084 .0110 .0118 'Beginning November 15, 1928. ^Approximate. 3Inflow of Gila River and San Carlos River. TABLE 3. Volumes of sediment deposited by 5-ft-elevation inter dinal slope, cross-sectional dimensions, shape, ve^e- vals in San Carlos Reservoir during different periods tation on exposed ground surface, and inflow chan Volume to next lower contour, Reservoir elevation in acre-ft nel geometry. The location of deposition is also regu (mean sea level) 1928-47 1947-66 1928-66 lated by concentration and particle size of sediment 2308 ...... 0 0 0 inflow, by rate of streamflow, and by the stage and 2365 ...... 6,060 0 6,060 2370 ...... 3,306 1 3,307 volume of water in storage. 2375 ...... 4,506 428 4,934 2380 ...... 4,696 1,435 6,131 THE EFFECT OF PHREATOPHYTES ON INFLOW CHANNELS 2385 ...... 4,869 2,143 7,012 2390 ...... 4,464 2,752 7,216 Phreatophytes can significantly reduce the con 2395 ...... 4,048 2,698 6,746 2400 ...... 3,551 2,656 6,207 veyance of reservoir inflow channels, particularly if 2405 ...... 3,097 2,528 5,625 2410 ...... 2,959 1,930 4,889 the stage of the water in the reservoir fluctuates 2415 ...... 2,784 1,492 4,276 2420 ...... 2,929 1,685 4,614 widely. The flat fertile plain at the upstream end of 2425 ...... 3,675 2,380 6,055 the reservoir pool has a shallow water table and is 2430 ...... 1,844 2,733 4,577 2435 ...... 1,653 2,581 4,234 periodically inundated, creating an ideal environ 2440 ...... 479 1,942 2,421 2445 ...... 553 1,655 2,208 ment for phreatophytes such as saltcedar. Inunda 2450 ...... 501 1,547 2,048 tion may kill the plants, but the prolific seed pro 2455 ...... 438 1,197 1,635 2460 ...... 81 1,165 1,246 duction and rapid growth of saltcedar quickly re 2465 ...... 247 499 746 2470 ...... 356 24 380 creates a dense thicket. When these sediment flats 2475 ...... 81 292 373 are exposed for extended periods of time, the salt- 2480 ...... 272 491 763 2485 ...... 122 766 888 cedar narrows the inflow channel by encroachment 2490 ...... -48 1,170 1,122 2495 ...... -30 1,036 1,006 and can eliminate a continuous channel. During the 2500 ...... 0 0 0 2505 ...... 0 0 0 period 1962-65, the inflow channel of the Gila River 2510 ...... 0 0 0 into the San Carlos Reservoir was blocked by a 2515 ...... 0 0 0 2520 ...... 0 0 0 combination of conditions including encroachment 2525 ...... 0 0 0 by phreatophytes on the sediment, a reduction in Total ...... 57,493 39,226 96,719 channel gradient, and plugging by the deposition of floating debris. Figures 6 and 7 show the sediment flats formed by common range of stage of the reservoir pool. As a deposition in the area above and below the con consequence, the surface-water dead storage capac fluence of the Gila and San Carlos Rivers. Tie ity of the reservoir was reduced 96 percent from upstream end of the reservoir pool was located in the 25,143 acre-ft (31 hm3) to 900 acre-ft (1.1 hm3) from area shown in these photographs during much of the November 1928 to August 1966 (see table 2). The period 1945-65. distribution of sediment is partly regulated by the During the period 1935-62 the location and aline- physical features of the reservoir, such as longitu ment of the Gila River channel did not change sigrif- N8 GILA RIVER PHREATOPHYTE PROJECT VOLUME OF SEDIMENT DEPOSITED WITHIN 1.52-METER- ELEVATION INCREMENTS, IN CUBIC HECTOMETERS I III I' 770 Elevation of maximum storage: Spillway gates fully raised 2,523 ft _ 2520 2510 765 EXPLANATION _ 2500 R&fMtVrl _ ":: ":i- ::- .:>. '.:..;::. :.. ,:^ -x j 760 2490 1958-47 _ HJ 2480 J _ 1947-66 7^5 LU _J < 2470 ill LU W ««ll Z 750 < < 2460 m LU LU > 2450 0 3 * *: *>£* CO mi\ LU 244 ° LU LL ':J'A':i-<^!^S^Ky%s£ZH^Af z 740 0 ^ 2420 nWMm'^IJJWiiiMiBMMMll LU 735 LU 2410 yi/in 1 1 if II 111 1 H! HI I tl I ITi f o[ Jtt!v?::S:H'-f|::-S;i;ff:l |-:| ? S Ct' IS ?' S ? | S| 1 ? :" .V f ]| 2400 £ '? ^ 1 f ; ^^^w? ?lslS^ Lj'J-.i| ; | ; ?',¥.:; J ?'S;|.^'g s.s| |; poo l 2 , 382.63 ft, := .5 ;; :;=:. :S. :- -f :> ::::.::,. :;|;::: I >::'.J. :=:; ;: ; :;. ::.. :>:: '":., : :.: .- :: .¥ :': : :: :: > : * ' ':' '.-. : ::: :":: ":- =: ,:=: : : :f :::::: S | / 730 / 2390 | ;? Sl1 ^?:?: :? :{] i-S £S I? |:1'£ :' ?' |i ::?, S:S>:j::|:S:^:S.|;-:||:;|;|; J.|: :| ;|.S3 ;Sc|K v:iS;;|| |: . ? :' 5' S | , |::::f"S:: $ !i'. J S'|j ' 2380 l::f i|"'?,? t 'US S-s: 1 s=" -6 ?'|: ::i.ii::ii;!:SI:;:tI:|- f'l£M' si 1 l-'l 1. f 1 .s :I-S '&&-. S x\:]::p;S',-| !:;] 725 5'j| if :; ; ;: , .-;; ;:; Jj'g .J. Q j; :? .J 5:S: j ::J: -f m'm&S &£&&£&$ S *'?: M M -¥S ;* S I^'SS^^M 2370 2365^ 721 2308*1 703 1000 2000 3000 4000 5000 6000 7000 8000 VOLUME OF SEDIMENT DEPOSITED WITHIN 5-FT-ELEVATION INCREMENTS, IN ACRE-FEET FIGURE 4. Vertical distribution of the volume of sediment deposited within 5-ft (1.5 m)-elevation intervals at San Carlos Reservoir for the periods 1928-47 and 1947-66. icantly as indicated by comparing figure 8 with exposure to sunlight are an excellent environment figure 9. The width of the channel was appreciably for saltcedar. This vigorous growth encroaches on reduced and natural levees had formed during this the channel and thus reduces the conveyance capa period, however. Figure 10 shows the levees along bility of the channel during flood flows. Wh«m flows the banks of the inflow channel of the Gila River exceed the conveyance capacity of the channel, the which had developed by August 1965. The river- excess water overflows the banks and inundates the banks with abundant water supply and extensive adjacent flood plain. Sediment is then deposited on ELEVATION, IN FEET ABOVE MEAN SEA LEVEL -» O oo > O H X O «! m H H oo § «' 0} (D ->Ul toUl -> CO n 01 Q>-r I I T o 3 ! ,!' H -> -> 10 o 01 o O Ul O (Jl O Ul O ELEVATION, IN METERS ABOVE MEAN SEA LEVEL 6N IL-6Z61 'VNOZIHV 'HIOAH3S3H SO1HVO NVS dO AHOXSIH OIOO1OHQAH N10 GILA RIVER PHREATOPHYTE PROJECT FIGURE 8. Aerial view of channel conditions of the Gila River upstream from the San Carlos River in 1935 7 years after the FIGURE 6. Aerial view looking downstream (west) on April 20, completion of Coolidge Dam. The upstream end of the reservoir 1965, showing the sediment flats at the confluence of the Gila pool is shown in the lower left. The Gila River flood plain shown and San Carlos Rivers within the San Carlos Reservoir. The in the photograph had been inundated by the reservoir pool reservoir pool, with water-surface elevation at 2,419.00 ft (737 m) during the period 1929-35. Soil Conservation Service photo above sea level and usable contents of about 60,000 acre-ft graph. (74 hm3), is shown in the upper right center of the photograph. The Gila River channel is at the lower right and the San Carlos River channel is at the right center. The dark areas are well- established saltcedar. FIGURE 7. Aerial view looking upstream (north) on April 20, 1965, showing the San Carlos River on the left and the Gila River on the right. The lower center part of this photograph FIGURE 9. Aerial view of conditions of a part of the Gila River overlaps the right center part of figure 6. The area shown in channel above the San Carlos River in June 1962. Flow in the figures 6 and 7 includes the area periodically inundated by river is from upper right to lower left. The channel is continuous, reservoir water during the period 1945-65. but a comparison of this photograph with figure 8 indicates that the width has been reduced and the riverbed has been consider ably elevated. Extensive ephemeral off-channel ponds are the flood plain because of decreased velocity of the shown in the vicinity of the abandoned railroad crossing. overbank flow. Intermittent channels and pools are formed on the flood plain and provide a surface Figure 11 shows a saltcedar thicket after the irrigation for the saltcedar. reservoir water has receded following an inundation HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 Nil ideal for subsequent germination and establishment of saltcedar growth. The plugging of the inflow channel of the Gila River during 1962-65 occurred within the 4.1-mi (6.6 km) reach shown in figure 12. The deposition of sediment and reduction in slope of the flood plain since construction of Coolidge Dam in 1928 are shown in figure 13. The constriction caused by the railroad fill at the abandoned railroad bridge site was partly responsible for the exceptional depth of sediment deposits and the resulting de crease in slope in this reach of flood plain. Deposition of sediments at the mouth of the San Carlos River may also have been responsible. The combination of a reduction in channel width due to encroachment by vegetation and a reduction in channel velocities due to reduced slopes ultimately caused the deposition of debris shown in figure 14. Logs and sediment formed FIGURE 10. View looking downstream (south) on August 18, a dam practically eliminating the conveyance capa 1965, at the Gila River flood plain from a point 2 mi (3.2 km) bilities of the channel. Saltcedar then became estab upstream from the mouth of the San Carlos River. The former lished in the debris and sediment to create an Gila River inflow channel extends from the lower left corner along the right side of the photograph. The natural levees and erosion-proof channel plug as shown in figure 15. vigorous bankside saltcedar are apparent. Deposition elevated The formation of a channel plug causes channel the channel above the surrounding flood plain. In the lower filling which quickly progresses upstream as indi foreground numerous channels cross the former main channel cated in figure 12. The upstream end of the debris at right angles. The water surfaces shown near the center of the plug deposited by a flood discharge during the period photograph are ephemeral off-channel ponds. The roadbed fill approach to the abandoned railroad bridge shows as a dark line July 15-22,1964, is shown in figure 16. Large concen in the center of the photograph. trations of debris are a characteristic of summer flood flows on the Gila River. As described by Burk- ham (1970), these flows originate from intense indi vidual thunderstorms which produce high rates of runoff from small tributary watersheds but only rarely do they produce large rates of flow on the main channel. The high rates on the tributaries strip debris from the watersheds, convey the debris to the Gila River, and thence downstream on what is generally a moderate flow in the Gila channel. The progress of the plugging phenomenon as shown in figure 12 was 1.5 mi (2.4 km) in 1963,1.8 mi (2.9 km) in 1964, and 0.8 mi (1.3 km) in 1965 and is primarily the result of summer flows. In the summer of 1965, a channel was excavated by dragline parallel to the plugged natural channel. The high discharge in the Gila River during December 1965 to May 1966 raised the water level in San Carlos Reservoir to an elevation which inundated most of the Gila River flood plain shown in figure 12. An FIGURE 11. Flood-plain conditions after the area was inundated excavated inflow channel has been maintained for by the reservoir pool. The water had been higher than the tree- the Gila River since 1966. tops, thus killing the saltcedar. The white bands on the dead tree stems are mud deposited during the reservoir recession. SEDIMENT TRAP EFFICIENCY Sediment trap efficiency is the ability of a reservoir of sufficient depth to kill the plants. The soggy to retain sediment and is expressed in percent of total ground conditions, obvious in the photograph, are incoming sediment (Gottschalk, in Chow, 1964). A N12 GILA RIVER PHREATOPHYTE PROJECT 110 25' 33 15' C A E L O S Plugging started 1962 ~ 33 10' Base from U.S. Geological Survey, San Carlos Reservoir 1:62,500,1962 EXPLANATION 2 MILES 60 0 1 3 KILOMETERS Distances along longitudinal axis of reservoir from Coolidge Darn, in CONTOUR INTERVAL 80 FEET thousands of feet DOTTED LINES REPRESENT 20-FOOT CONTOURS DATUM IS MEAN SEA LEVEL Oct. 1964 \ Location of channel plug on date shown FIGURE 12. Extent of channel plugging in Gila River on indicated dates. sediment trap efficiency of 83 percent was predicted ment was expected to pass through in suspension or for San Carlos Reservoir by the U.S. Army Corps of by sluicing. Engineers (1914, p. 30). The remainder of the sedi There are no records of sediment inflow or outflow HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N13 DISTANCE FROM COOLIDGE DAM, IN KILOMETERS 13 14 15 16 17 18 19 20 21 2460 748 <2 450 111 - 746 W Z W 2440 744 LLJ - 742 > O CD 2430 < - 740 LU 2420 - 738 - 736 FIGURE 15. Downstream view on July 15, 1965, of a reach of the 2410 Gila River channel which had been plugged in 1964. Saltcedar -Abandoned railroad crossing 734 is becoming established in the former channel bottom. 732 2400 43 50 60 70 DISTANCE FROM COOLIDGE DAM, IN THOUSANDS OF FEET FIGURE 13. Profiles along the longitudinal axis of San Carlos Reservoir showing changes in bed elevations and slope with in the reach of channel plugging. FIGURE 16. Aerial view of channel plugging in the Gila River on July 22, 1964. Flow is from right to left. FIGURE 14. View of the Gila River looking north from a point Carlos Reservoir, according to Gottschalk (in Chow, 2.6 mi (4.2 km) upstream from the mouth of the San Carlos River photographed in September 1964. The debris in the channel is 1964, fig. 17-1-6). part of a recently deposited channel plug. Flow is from right to ANALYSIS OF SEDIMENT DATA left. The U.S. Army Corps of Engineers reported (1914, p. 29-30) predictions of the volume of sediment for San Carlos Reservoir, so trap efficiency is not deposition based in part on streamflow records and known; it probably exceeds the predicted 83 percent. on 15 sediment samples collected from deposits Trap efficiency should be 96 percent or more at San along the Gila River. Streamflow records of 1890 and N14 GILA RIVER PHREATOPHYTE PROJECT 1895-1912 indicate that the mean annual streamflow period. The storage loss for any time interval is was 346,000 acre-ft (427 hm3). In the 1914 report, the estimated as the product of this mean concentration predicted specific weight of deposited sediments was and the interval streamflow. (See table 2 for period 70 lb/ft3 (1,120 kg/m3), predicted volume of deposi rates for San Carlos Reservoir.) This storage loss can tion at 100 percent trap efficiency was 1.3 percent of be obtained graphically for San Carlos Reservoir by total streamflow, and the predicted trap efficiency using accumulated streamflow and figure 17. The was 83 percent. Based on these predictions and inset in figure 17 shows measured change in storage measured streamflow, the estimated mean annual compared to measured streamflow for each of the volume of reservoir sediment deposits was 3,740 acre- periods between surveys. ft (4.6 hm3). The method of interpolating storage change Records of streamflow from November 1928 adopted for use in this report employs the equiva through August 1966 show the mean annual stream- lency of the loss in surface-water storage capacity flow was 216,120 acre-ft (266 hm3), or 63 percent of and the change in sediment deposits. A procedure for the predicted flow. The mean annual volume of simulating deposition was developed and used to sediment deposition was 2,553 acre-ft (3.15 hm3), or estimate the sediment volume deposited each water 68 percent of the predicted volume. year. The development of this procedure and its A mean sediment concentration for stream dis application in providing yearly capacity ratings is charge can be estimated from measured volumetric described in the section "Development of Surface- changes in reservoir deposits because a reservoir is a Water Storage-Capacity Ratings." collector for fluvial sediment moved by all transport methods. The mean sediment concentration com puted from the information in the 1914 report is HYDROLOGY 14,478 ppm (14,615 mg/1). The mean concentration WATER-BUDGET EQUATION from November 1928 through August 1966 is 13,684 A water budget is used in this report for presenta ppm (13,808 mg/1) when computations are made tion of an historical accounting of the hydrology of using measured streamflow and sediment deposition San Carlos Reservoir for water years 1931-71. The and when estimates of trap efficiency, specific water-budget equation for San Carlos Reservoir is weight of deposits, and specific gravity are 96 per JT~ ~~ C-/Z7* "" C/ZT'T1 cent, 70 lb/ft3 (1,120 kg/m3), and 2.65, respectively. JG + 'S G FJ FJ / On a volumetric basis, sediment accumulated at ± ASp ± AS» = 0. (1) an average rate of 0.0118 (volume of sediment depos ited/volume of streamflow) from November 1928 to August 1966. The rates for the periods between The components of the water budget are identified surveys, chronologically, are 0.0198, 0.0059, 0.0084, as follows: and 0.0110, as listed in table 2. =Gila River inflow at Calva, IS -San Carlos River inflow at Peridot, INTERPOLATION OF ELEVATION-CAPACITY Ip ^precipitation input over the lake surface, RATINGS BETWEEN CAPACITY SURVEYS -ground-water inflow, Elevation-capacity relations were defined for each tributary inflow downstream from the reservoir survey. Significant changes in these rela Gila and San Carlos River tions between surveys required the development of a gaging stations, systematic method of interpolating changes during OG =Gila River outflow below Coolidge Dam, the periods. ^evaporation from the lake surface, The simplest method of interpolation is to pro-rate =evapotranspiration from the exposed storage capacity change by time between consecu land surface of the reservoir, tive surveys. This method of interpolation can be =change in surface-water storage, and applied either to change in total storage capacity or ^change in bank storage. to change by increments of the total reservoir storage. Neither the evapotranspiration nor the change in Interpolation can also be made by pro-rating the bank storage was measured. Before evapotranspira change in storage capacity according to streamflow. tion could be computed by the water-budget equa Because the loss in storage capacity is the volume of tion, estimates of bank storage were necessary. A dis sediment deposition, this method is basically the use cussion of the evaluation of each water-budget com of a mean sediment concentration computed for a ponent is presented in the following sections. HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N15 ACCUMULATED STREAMFLOW, Q, IN CUBIC KILOMETERS 345678 120 I______I______I I I I I I Accumulated streamflow, Q, in cubic kilometers 01 2345 - 140 I I I 01234 Accumulated streamflow, Q, in millions of acre-feet 1947 EXPLANATION 1935 o Year of capacity survey ACCUMULATED STREAMFLOW, Q, IN MILLIONS OF ACRE-FEET FIGURE 17. Relation between accumulated decrease in storage capacity and accumulated streamflow by capacity survey periods. Inset shows relation of storage capacity change and streamflow for each period. SURFACE FLOW GILA RIVER AND SAN CARLOS RIVER INFLOW Records of streamflow into the reservoir for the 1929-71 water years were taken from U.S. Geological Survey Water-Supply Papers 1313 and 1733 and from U.S. Geological Survey annual state reports of Arizona streamflow. Inflow records used in this study are primarily those for the Gila River at Calva and the San Carlos River at Peridot. Some of the 1929 inflow data were estimated from reservoir outflow data and changes in reservoir storage. Additional sources of Gila River streamflow information in clude reports by Burkham (1970) and the U.S. Army Corps of Engineers (1914). WATER YEAR Figure 18 shows the total annual streamflow into FIGURE 18. Annual combined Gila River and San Carlos River the reservoir for water years 1929-71. The stream- inflows to San Carlos Reservoir for water years 1929-71. flow data are included in table 17. The mean annual inflow for this period was 214,940 acre-ft (265 hm3), is less than the mean because of the influence of and the annual median was 159,000 acre-ft (196 these infrequent extreme annual totals. hm3). The large difference between the mean and Mean annual streamflow, 1929-71, into the reser median values is caused by infrequent years of voir was 33,450 acre-ft (41 hm3) for the San Carlos extremely high flow. Of the annual totals 67 percent River and 181,490 acre-ft (224 hm3) for the Gila River. N16 GILA RIVER PHREATOPHYTE PROJECT The San Carlos River, with 8.6 percent of the con INFLOW, IN CUBIC HECTOMETERS tributing area, produced 15.6 percent of the total 200 400 600 800 1000 1200 i u - streamflow into the reservoir. Annual streamflow of CO Q DC 9 the San Carlos River ranged from 6.2 percent of the < 8 - total streamflow into the reservoir in 1959 to 40 >. 1 - u. 6- percent of the total streamflow in 1956. 0 5 - DC 4 _ A generally declining trend in annual streamflow LU c ro CQ 3 - I T3 coincided with a similar declining trend in annual ro 1 2 - 0) TABLE 7. Estimated tributary inflow into San Carlos Reservoir Estimated seasonal runoff, in acre-ft Based on runoff Prom rainfall- Average of measured for runoff relation, Based on 9 columns 3 Water year part of the area equation 2 acre-ft/mi2 and 4 (1) (2) (3) (4) (5) 1931 ...... 3,660 3,510 3,580 1932 ...... 0 3,510 1,760 1933 ...... 1,420 3,510 2,460 1934 ...... 1,800 3,510 2,660 1935 ...... 4,520 3,510 4,020 1936 ...... 0 3,510 1,760 1937 ...... 0 3,510 1,760 1938 ...... 0 3,510 1,760 1939 ...... 0 3,510 1,760 1940 ...... 0 3,510 1,760 1941 ...... 10,470 3,510 6,990 1942 ...... 1,320 3,510 2,410 1943 ...... 890 3,510 2,200 1944 ...... 8,640 3,510 6,070 1945 ...... 2,520 3,510 3,010 1946 ...... 6,190 3,510 4,850 1947 ...... 3,600 3,510 3,550 1948 ...... 1,650 3,510 2,530 1949 ...... 1,860 3,510 2,680 1950 ...... 1,550 3,510 2,530 1951 ...... 2,340 3,510 2,930 1952 ...... 1,720 3,510 2,620 1953 ...... 0 3,510 1,760 ...... 11,460 3,510 7,430 MONTH 1954 ...... 1955 ...... 10,420 3,510 6,960 1956 ...... 0 3,510 1,760 FIGURE 20. Mean monthly flow as a percent of mean annual 1957 ...... 0 3,510 1,760 flow for the Gila and San Carlos Rivers. 1958 ...... 9,330 3,510 6,420 1959 ...... 8,330 3,510 5,920 1960 ...... 4,370 3,510 3,940 1961 ...... 6,670 3,510 5,080 usually occurs only during the summer storm sea 1962 ...... 2,460 3,510 2,980 son, July through October. 1963 ...... 3,660 3,510 3,580 1964 ...... 3,320 11,730 3,510 7,620 Tributary inflows from 72.6 mi2 (188 km2) of the 1965 ...... 3,860 370 3,510 1,940 1966 ...... 1,600 13,660 3,510 8,580 gaged tributary area entering the reservoir below the 1967 ...... 8,380 8,100 3,510 5,800 1968 ...... 1,210 0 3,510 1,760 Calva gaging station were determined for the sum 1969 ...... 1,250 1,460 3,510 2,480 mer storm seasons of 1964-71 (Burkham, 1976). 1970 ...... 470 3,620 3,510 3,560 1971 ...... 11,930 4,310 3,510 s.gi') Totals of seasonal runoff from this area, and runoff per unit area, are listed in table 6. Mean ..... 1 3,998 2 3,758 2 3,510 2 3,6? 1 'Eight (8) year mean. Several methods were used to estimate seasonal 2Forty-one (41) year mean. runoff from all areas tributary to the reservoir. In the first method, runoff was assumed to be spatially con table 6. The regression equation relating rainfall and stant. The seasonal runoff values per square mile for 1964-71, from table 6, were multiplied by the 390-mi2 runoff data was (1,010 km2) tributary area and the results listed in Q = -0.382 + 0.093P, where P > 4, (2) column 2 of table 7. The tributary runoff estimates of column 3 in table with rainfall, P, and runoff, Q, given in inches. The 7 are results of a rainfall-runoff correlation. Rainfall regression line and the data used to develop equrtion was measured for the Gila River Phreatophyte Proj 2 are plotted in figure 21. The equation was used to ect in gages located near the downstream ends of the estimate runoff from the 390-mi2 (1,010 km2) tribu tributary streams. The tributary runoff data is from tary area using seasonal precipitation at San Carlos Reservoir. The correlation between seasonal rainfall TABLE 6. Tributary inflow into the San Carlos Reservoir along a reach of the Gila River measured on the Gila River Phreatophyte Project Seasonal tributary runoff Mean seasonal runoff area and seasonal rainfall at the San Carlos Reser Water year (acre-ft) (acre-ft/mi2) voir weather station is poor. Runoff estimates in 1964 616 8.5 column 3 of table 7 are probably poor partly because 1965 1 732 9.9 1966 301 4.1 of this high spatial variability in rainfall intensities. 1967 1,560 21.5 1968 228 3.1 Burkham (1974) indicated that the mean seasonal 1969 229 3.2 1970 86 1.2 runoff from all the study watersheds for the period 1971 2,220 30.6 1963-71 was about 9 acre-ft/mi2 (0.004 hmWm2). Includes an additional gaged area of 1.0 mi2 (2.59 km2 ). Seasonal tributary runoff into the reservoir using N18 GILA RIVER PHREATOPHYTE PROJECT SUMMER RAINFALL,P, IN MILLIMETERS eluded in the water budget. Mean monthly dis 0 50 100 150 200 250 300 charges of the Gila River below Coolidge Dam are UJ i i i i i i I 0.7 ^ ...... o shown in table 8 and are an indication of seasonal z 0.6 - 150 Ol demands of water for irrigation. z / - The peak instantaneous discharge since the dam - 0.5 u- / was constructed was 1,350 ftVs (38 mVs) on July 28, LL 0.4 Q=-0.382 + 0.093P S - 100 3 LL 1952. No flow occurred several times prior to 1938, O (Q and P in inches) / Z 0.3 cc when the gaging station was about 0.2 mi (0.3 km) D « o: 0.2 - -50 upstream from its present location. The minimum o: 5 HI D flow after 1938 was about 0.4ftVs (0.011 mVs) which 0.1 - / W includes the discharge of Warm Springs, a tributary -> 0 .I i V i i i i i L- n 12 to the Gila River. SUMMER RAINFALL,P, IN INCHES GROUND-WATER INFLOW FIGURE 21. Relations between measured rainfall and tributary From 1963 to 1972, ground-water data were col runoff for summer seasons 1964-71 from 72.6 mi2 (188 km2) of lected and analyzed as part of the Gila River Phroato- area tributary to San Carlos Reservoir. phyte Project. The part of the Gila River F^re- atophyte Project area within the boundaries of the reservoir (fig. 1) included an 8 mi (13 km) reach of the this rate is 3,510 acre-ft (4.33 hm3), as shown in Gila River flood plain below the Calva gaging column 4 of table 7. station. Computations of ground-water inflow into These methods do not accurately estimate sea the reservoir were based on results of the project's sonal tributary runoff to San Carlos Reservoir for ground-water analyses (Hanson and others, 1972; each year. However, the individual means at the Hanson, 1972). bottom of column 2 through column 4 of table 7 The geologic water-bearing units along the Gila deviate less than 10 percent from the average of the River have been identified as alluvium and basir fill. means. The close agreement of mean values suggests The alluvium was deposited in a trench incised in the that the 41-year water budget is improved by the basin fill. Two components compose the alluvium: addition of tributary runoff estimates. flood-plain alluvium and terrace alluvium. Terrace The average of the estimates from columns 3 and 4 alluvium covers the basin fill in the trough and of table 7 was selected somewhat arbitrarily to define extends above the flood plain on the adjoining the seasonal totals to include in the water budget and slopes. Flood-plain alluvium overlies the terrace column 5 of table 7. The estimates in column 3 alluvium in the flood-plain region and averages assume that a seasonal variability of precipitation is about 50 ft (15 m) in depth and 5,000 ft (1,500 n) in uniform in space. The estimates in column 4 assume width. The basin fill extends a considerable distance runoff is uniform in space and time. up the slopes beyond the terrace alluvium. GILA RIVER OUTFLOW Water enters the basin fill on the mountain slopes About 78 percent of all inflow into San Carlos and moves generally toward the flood plain. Where Reservoir is released downstream into the Gila the basin fill is in contact with the alluvium, ruffi- River. Releases are based on reservoir supply and cient head exists to create a slow upward movement the needs of the San Carlos Project near Coolidge, of water from basin fill to the overlying alluvium. Ariz. Records of releases are based on river-stage Another ground-water source into the reservoir is data obtained at a flume 0.4 mi (0.6 km) downstream from Coolidge Dam, at the U.S. Geological Survey TABLE 8. Mean monthly discharge of the Gila River below gaging station, Gila River below Coolidge Dam, Coolidge Dam, 1931-71 Ariz. Streamflow records have been available at this Month Discharge, in acre-ft station from 1939 to 1971 and near this location for Oct ...... 8,580 much of the period 1899-38.1 ...... 5,980 ...... 6,640 Discharge data for water years 1931-71 are in- ...... 3,160 Feb ...... -...... --.-- ...... 6,920 ...... 16,330 'Quoting from the 1971 annual report of U.S. Geological Survey surface-water records, ...... 21,140 Gila River below Coolidge Dam, Arizona, "Records available. July to October 1899, ...... 20,800 April 1900 to March 1902, July to September 1902, December 1902 to December 1904, ...... 24,050 January to May 1905 (gage heights only), June to November 1905, August 1910 to Feb July ...... 25,880 ruary 1911 (gage heights only), April 1914 to current year. Published as 'at San Carlos' ...... 21,840 1899-1911, as 'near San Carlos' 1914-1926, and as 'at Coolidge Dam' 1927-38." ...... 18,110 HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N19 downvalley flow through the saturated flood-plain TABLE 9. Annual (water year) precipitation, in inches, at S«.n alluvium. A small amount of ground water enters the Carlos Reservoir, 1931-71 reservoir from the alluvium deposited by tributary Water Water Water streams but is considered insignificant. year Precipitation year Precipitation year Precipitation 1931 ...... 15.57 1945 ...... 13.53 1959 ...... 11.74 Downvalley ground-water movement in the Gila 1932 ...... 14.19 1946 ...... 11.56 1960 ...... 15.36 1933 ...... 13.49 1947 ...... 9.45 1961 ...... 11.02 River flood plain alluvium has been computed at 5.1 1934 ...... 6.46 1948 ...... 9.27 1962 ...... 13.34 acre-ft (0.0063 hm3) per day (Hanson, 1972, p. 25). 1935 ...... 19.64 1949 ...... 13.63 1963 ...... - ...... 14.87 1936 ...... 11.61 1950 ...... 11.14 1964 ...... 12.94 Hanson, Kipple, and Culler (1972, p. 317) estimated 1937 ...... 12.98 1951 ...... 11.87 1965 ...... 14.00 1938 ...... 11.75 1952 ...... 18.61 1966 ...... 27.17 basin-fill inflow along the Gila River at 0.82 acre-ft 1939 ...... 10.65 1953 ...... 10.81 1967 ...... 13.34 (0.0010 hm3) per day per 1,000 acres (4.05 km2). This 1940 ...... 12.50 1954 ...... 19.16 1968 ...... 16.53 1941 ...... 30.53 1955 ...... 14.08 1969 ...... 13.41 is equivalent to about 0.50 acre-ft (0.00062 hm3) per 1942 ...... 12.94 1956 ...... 9.05 1970 ...... 13.28 1943 ...... 11.82 1957 ...... 11.17 1971 ...... 8.85 day per downvalley mile, or 10.5 acre-ft (0.0129 hm3) 1944 ...... 14.96 1958 ...... 19.87 per day over the 21-mi (33.8 km) reach from the Calva streamflow station to the dam. The sum of the voir for the period ranged from 0.21 in. (5.3 mm) in alluvial inflow and basin-fill inflow is 15.6 acre-ft May to 2.19 in. (56 mm) in August. Seasonal trends (0.0192 hm3) per day in the Gila River part of the are evident in the mean monthly precipitation data reservoir. of table 10. The monthly extremes, also listed in table Flood-plain alluvial flow (q) for the San Carlos 10, indicate the large variation in precipitation. Tl e River at Peridot was computed from the equation mean precipitation for the summer season (July q = K»m (3) through October) is 5.89 in. (150 mm), or 42 percent of the mean annual total. Precipitation for the remain where K is the hydraulic conductivity estimated for der of the year averaged 7.98 in. (203 mm) during the Gila River flood-plain alluvium at 5,200 gal/day/ft2 41 years. (212 mVday/m2) and is assumed the same for the The volume of daily precipitation into the reservoir flood-plain alluvium along the San Carlos River, m is was computed as the product of daily precipitation the depth of alluvium and is estimated to be 30 ft (9 measured at the San Carlos Reservoir weather sta m), wis the alluvial width of about 2,800 ft (850 m), u tion and the surface area of the water in storage for is the slope of the downvalley ground-water surface the day. Water year volumes of precipitation fallirg and is estimated to be equal to the downvalley flood- onto the water in storage are listed in table 17. From plain slope of 0.00275. Equation 3 gives q equal to 3.7 1931 through 1971, the total accumulated volume of acre-ft (0.0046 hm3) per day. The reach of the San precipitation falling directly onto the water surface Carlos River from the Peridot gaging station to the of the reservoir was computed as 203,900 acre-ft (251 river mouth is 9.2 mi (14.8 km). Assuming that the hm3), about 2.2 percent of reservoir input from z 11 San Carlos River flood plain has the same basin-fill sources. inflow per unit area as the Gila River flood plain, the inflow per downvalley mile per day is 0.50 acre-ft EVAPORATION (0.00062 hm3) times the ratio of alluvium widths Evaporation from San Carlos Reservoir is signifi (2,800 ft/5,000 ft) for the two flood plains, or 0.28 acre- cant because of the warm, dry environment in which ft (0.00034 hm3) per mile per day. Basin-fill inflow the reservoir is located. Evaporation, as used in tb«s along the 9.2 mi (14.8 km) San Carlos River reach is San Carlos Reservoir water budget, is computed as therefore about 2.6 acre-ft (0.0032 hm3) per day. The direct loss from the surface area of the reservoir pool. sum of the basin-fill and alluvial ground-water con Daily pan evaporation data for water years 1931- tribution from the San Carlos River basin is 6.3 acre- 71 were available for the weather station at San ft (0.0078 hm3) per day. Carlos Reservoir. Saturday and holiday pan evapor ation readings were omitted from 1930 through Apr I PRECIPITATION 1948. The history of changes to the evaporation pan Records of precipitation at San Carlos Reservoir at the dam is available in the National Weather were obtained from National Weather Service pub Service publication, "Substation History for lications and log books at Coolidge Dam. Table 9 Arizona." includes annual precipitation totals for water years Reservoir pool evaporation is computed as tl ^ 1931-71. The mean annual precipitation was 13.87 product of measured pan evaporation and the evapo in. (352 mm) and ranged from 6.46 in. (164 mm) in ration pan coefficient. A daily volume of computed 1934 to 30.53 in. (775 mm) in 1941. pool evaporation is the product of daily pan evapora Mean monthly precipitation at San Carlos Reser- tion, the pan coefficient, and daily surface area of th<* N20 GILA RIVER PHREATOPHYTE PROJECT TABLE 10. Mean monthly precipitation and monthly extremes (1931-71) at San Carlos Reservoir Oct. Nov. Dec. Feb. Mar. May July Sept. Mean monthly precipitation, 0.88 1.07 1.80 1.44 1.33 1.28 0.52 0.21 0.33 1.62 2.19 1.20 Minimum monthly precipitation, .0 .0 .0 .0 .0 .0 .0 .0 .0 .08 .25 .0 Maximum monthly precipitation, 4.28 3.73 8.53 4.00 3.26 6.02 2.29 .98 1.40 4.68 5.99 3.61 pool. Records of daily pool evaporation volumes have is shown in the upper portion of figure 22 for water been published in annual reports of the Gila River years 1931-71. Mean annual (water year) pan evapo Water Commissioner beginning in 1936. A pan coef ration was 97.3 in. (2,470 mm), and water-year ficient of 0.7 was used by the Gila River Water Com extremes ranged from the 1941 low of 83.6 in. (2,120 missioner in computations of pool evaporation. mm) to the high in 1939 of 111.4 in. (2,830 mm). In December 1963, the U.S. Geological Survey At San Carlos Reservoir, annual pan evaporation established a station about 350 ft (107 m) from the appears to have followed a downward trend, as San Carlos Reservoir weather station to collect indicated by the plot of 5-year moving averages radiation and air temperature data for use in comput shown in figure 22. During this same 41-year period, ing pool evaporation by energy-budget and mass- annual precipitation also indicates a decreasing transfer methods. Wind movements and water- trend (Burkham, 1970). This seems contradictory surface temperature data were recorded on raft- because the decrease in precipitation implied that mounted instruments at either one or two locations evaporation potential might have increased. T N US, it on the lake; the number and location of rafts was was necessary to investigate further pan evapora determined by the surface area of the pool. Stream- tion data at San Carlos Reservoir. flow temperature profiles (thermal surveys) of the Pan evaporation is affected by the conditions of pool were made every 2 or 3 weeks to measure both the pan and the immediate environment, condi changes in stored energy. tions which can change independently of char ges in The energy-budget equation is based on the prin climate. In an attempt to evaluate the reliability of ciple of conservation of energy. Measurements are the pan evaporation data at San Carlos Reservoir, made of most of the incoming and outgoing energy the data were compared with pan evaporation data components and of changes in stored energy in the at other Arizona stations. Figure 23 compares the 5- water body. The unmeasured energy remaining as a year moving average of pan evaporation at San residual of the energy-budget equation includes Carlos Reservoir with the 5-year moving average of energy for the evaporation process, energy of sensi ble-heat exchange, and energy advected by evapo rated water. The energy-budget method has been described by Anderson (1954). In the mass-transfer method, evaporation is treated as the turbulent transport of water vapor in the boundary layer overlying the water surface. The method requires data of wind speed, vapor pressure of the air, and vapor pressure of saturated air at water-surface temperature. A detailed description of the mass-transfer method is available in Marciano and Harbeck (1954). O) Computations of lake evaporation were made by WATER YEAR energy-budget and mass-transfer methods for 93 EXPLANATION periods during 1964-71. Occasional incomplete data Annual pan evaporation reduced the number of periods of reliable data to 72. A pan coefficient was computed for each period. The 5-year moving average of pan evaporation average pan coefficient was 0.80 for the 8 years of Adjusted annual evaporation for reservoir record. FIGURE 22. Evaporation at San Carlos Reservoir for water years Annual pan evaporation at San Carlos Reservoir 1931-71. HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N21 the mean of annual pan evaporation for Mesa, Roosevelt Lake, and Tucson (Univ. of Ariz.). The trend at San Carlos Reservoir is downward for much of the 1931-71 period as opposed to an upward trend at the other stations. Changes in the relation be tween the San Carlos Reservoir data and the me, CUMULATIVE PAN EVAPORATION-SAN CARLOS RESERVOIR, IN METERS 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 320 I .I I. I.I.I .I I I , I.I.I .I 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 CUMULATIVE PAN EVAPORATION-SAN CARLOS RESERVOIR, IN FEET FIGURE 24. Double-mass diagram of cumulative pan evaporation for San Carlos Reservoir and mean of Mesa, Roosevelt Lake, and at Tucson (Univ. of Ariz.) for water years 1931-71. N22 GILA RIVER PHREATOPHYTE PROJECT from computed lake evaporation at San Carlos Res records of stage and usable surface-water contents ervoir and the average of pan evaporation for Mesa, are published in the annual reports of the Gila River Roosevelt Lake, and Tucson (Univ. of Ariz.). This Water Commissioner. Usable surface-water storage coefficient was assumed applicable in periods 1 and 2 data are also contained in annual U.S. Geological also, when computing San Carlos Reservoir evapora Survey reports. Figure 25 shows beginning-of-month tion on the basis of pan evaporation at the other reservoir stages for water years 1929-71. Total three stations. San Carlos Reservoir pan coefficients surface-water storage and change in surface-water for periods 1 and 2 were 0.61 and 0.66, respectively, storage were obtained from the yearly elevation- obtained from the relation: San Carlos Reservoir pan capacity ratings and are shown in table 18 by water coefficient for a period equals computed lake evapo year. The derivations of these ratings are described ration divided by measured pan evaporation. Periods in the section "Development of Surf ace- Water 1 and 2 pan coefficients were applied to annual pan Storage-Capacity Ratings." evaporation measured at San Carlos Reservoir to compute annual lake evaporation. The annual pan TABLE 11. Evaporation at San Carlos Reservoir by water year 1931-71 evaporation, pan coefficients, and corresponding Pan Computed computed lake evaporation amounts for the 41-year evaporation lake evaporation study period are included in table 11. Computed lake Water year (in.) Pan coefficient (in.) 1931 ...... 94.47 0.61 57.63 evaporation is compared with the San Carlos Reser 1932 ...... 96.46 .61 5884 voir pan evaporation in figure 22. The annual lake 1933 ...... 105.45 .61 6432 1934 ...... 109.86 .61 67.01 evaporation expressed as volumetric loss is given in 1935 ...... 95.64 .61 5834 1936 ...... 103.00 .61 62.83 table 17. Mean annual depth of evaporation was 1937 ...... 107.54 .61 6560 69.95 in. (1,780 mm) and represents 10.5 percent of 1938 ...... 107.56 .61 6561 1939 ...... 111.35 .66 7349 the outflow from the reservoir. Mean monthly depths 1940 ...... 101.83 .66 67.21 1941 ...... 83.64 .66 5520 of evaporation from the lake are shown in table 12. 1942 ...... 94.34 .66 62.26 Monthly differences between the computed pan 1943 ...... 101.13 .66 66.75 1944 ...... 98.73 .66 65.16 coefficients shown in table 12 are caused primarily 1945 ...... 100.81 .66 66.53 1946 ...... 104.80 .66 69.17 by changes in available energy. There was not 1947 ...... 104.20 .66 68.77 1948 ..... 106.18 .66 70.08 sufficient confidence in the computed monthly pan 1949 ...... 98.30 .66 64.88 coefficients for use in computations of lake evapora 1950 ...... 98.68 .66 65.13 1951 ...... 98.82 .80 7S.06 tion, although it is evident that the relation between 1952 ...... 90.55 .80 72.44 1953 ...... 94.84 .80 75.87 pan evaporation and lake evaporation is subject to 1954 ...... 93.73 .80 74.98 seasonal change. 1955 ...... 91.49 .80 73.19 1956 ...... 100.35 .80 8C.28 1957 ...... 96.54 .80 77.23 WATER STAGE AND SURFACE-WATER STORAGE 1958 ...... 89.03 .80 71.22 AT SAN CARLOS RESERVOIR 1959 ...... 97.63 .80 IS. 10 1960 ...... 99.30 .80 7C.44 Prior to January 15, 1937, water stage was deter 1961 ...... 94.60 .80 7E.68 1962 ...... 94.63 .80 7S.70 mined by use of reference points of known elevation 1963 ...... 89.13 .80 71.30 1964 ...... 94.81 .80 75.85 on a series of stakes. A continuous record of lake 1965 ...... 86.74 .80 6£.39 stage was made from January 1937 through 1971 1966 ...... 88.58 .80 7C.86 1967 ...... 93.12 .80 74.50 using a water-stage recorder. Daily stage records 1968 ...... 91.39 .80 7S.11 1969 ...... 92.56 .80 74.05 were applied to the elevation-capacity relations (fig. 1970 ...... 91.19 .80 72.95 3) to obtain daily reservoir storage contents. Daily 1971 ...... 97.47 .80 77.98 TABLE 12. Mean monthly evaporation and mean monthly pan coefficients for San Carlos Reservoir Month ...... Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Mean monthly lake evaporation in inches, 1931-71 ...... 5.01 2.66 1.57 1.73 2.52 4.42 6.57 9.03 10.58 10.28 8.46 7.12 Mean monthly pan coefficients from energy- budget computations, 1964-71 ...... 88 1.00 1.05 .74 .66 .68 .65 .69 .75 .79 .79 .86 Mean monthly pan coefficients from mass- transfer computations, 1964-71 ...... 90 1.10 .93 .71 .68 .66 .66 .70 .71 .83 .82 .79 FIRST-OF-MONTH ELEVATION, IN FEET ABOVE MEAN SEA LEVEL £k£k£k£iUl COCOJ^JiJiJ^JiUl COCOJiJiJiJiJiOl OOOOO OOOOQOOO OOOOOOOO i r (0 ( (0 *> ^X M O ^^ (0 N24 GILA RIVER PHREATOPHYTE PROJECT The highest reservoir stage of record (1929-71 ~pl 22 water years) was 2,501.62 ft (762.49 m) above mean 2500 pi 66 - 760 sea level on March 18, 19422. Usable surface-water 1- 2490 - UJ 193] 292 1 storage at that elevation was 819,200 acre-ft (1,010 £ -1 2480 UJ 317 I 194| hm3) using 1947 capacity tables. This storage is -UJ 247 ° 2Tl| _f-J 349| about 83 percent of the usable surface-water storage < < 2460 - 750 303| << capacity at 2,511 ft (765 m). Other peak stages 549 UJ Z 550 recorded were 2,491.17 ft (759.31 m) in 1968 and 377 - 745 2 ^ 2440 2,477.30 ft (755.08 m) in 1966. Usable surface-water 616 Z ^ 2430 565 storages at these elevations were 643,324 acre-ft (793 9Oil - 740 1,073 | hm3) and 417,673 acre-ft (515 hm3) using 1966 H o 2420 1,056 i=o >< 2410 c336 elevation-capacity tables. c335 UJ 2400 583 1 The minimum stage has fallen to, or below, the 7811 . "1 lowest outlet elevation of 2,382.63 ft (726.22 m) at ,035 i 3091 some time during 14 of the 43 years of record. At other 2,461 1 c3 O O O oooooooooc > times, inflow was barely sufficient to keep the pool O O O oooooooooc> CM USABLE SURFACE-WATER STORAGE, IN 100,000 ACRE FEET (4) FIGURE 28. Percentage of time usable surface-water storage at The rate of change in bank storage is dependent San Carlos Reservoir equaled or exceeded a given volume for upon the change in surface-water storage, ASg, so it water years 1929-71. is important that ASg be small for a month or more before and after the evaluation period. Table 14 Sy is the total water in storage, illustrates the application of equation 4 in computing fig is water contained in surface-water storage, ASg for the winter period January through April of fig is the water contained in bank storage, and 1965. A indicates the change in an associated stor ASg was determined for each of 23 winter periods age term. of significant ASg increases. ASg was not deter Inflow and outflow from bank storage can be mined for periods of decreasing Sg because all computed by use of combined water-budget and periods of a significant decrease in Sg corresponded modeling methods for some reservoirs, as demon to periods of high evapotranspiration rates. strated by Simons and Rorabaugh (1971). At San Several procedures were used to investigate the TABLE 13. Percentage of time that available monthly surface-water storage was less than amount shown Usable surface-water storage, in acre-ft Percentage of time Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sepf.. 25 6,820 3,150 11,200 8,700 20,100 29,100 35,700 21,000 12,700 950 5,000 8,2"^ 50 ...... 50,300 48,000 46,000 55,000 93,400 104,000 113,000 115,000 97,000 70,100 44,000 47,0^ 75 ...... 113,000 103,000 107,000 138,000 198,000 194,000 260,000 235,000 203,000 165,000 140,000 116,0^ 100 ...... 689,000 744,000 752,000 802,000 835,000 843,000 841,000 816,000 779,000 727,000 676,000 659,0^ TABLE 14. Example of water budget used to determine change in bank storage Month Surface-water Change in Change in Change in Water surface Change storage, surface-water total storage, bank storage, (water year 1965) stage in stage Sp storage, A°S# Inflow2 Outflow3 Asy4 As^j5 (ft)1 (ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) 2,407.47 5.88 29,790 15,464 18,986 619 18,367 2,903 Feb ...... 2,413.35 5.28 45,254 16,446 24,840 4,810 20,030 3,584 Mar ...... 2,418.63 .33 61,700 1,069 17,327 14,715 2,612 1,543 2,418.% -.45 62,769 -1,458 10,642 11,748 -1,106 352 2,418.51 61,311 Jan-Apr 11.04 31,521 39,903 8,382 AsB/ft = 759 acre-ft/ ft Average stage = 2,412.99 ft AsB/AsT = .210 Average Sn = 45,550 acre-ft AS R/ASn = .266 Elevation corre sponding to average S_ = 2,413.45ft 'Values for beginning and end of month. 2Inflow is the sum of Gila River inflow, San Carlos River inflow, precipitation on water surface, and ground-water inflow. 'Outflow is the sum of Gila River outflow and evaporation. 4 A/Sy equals inflow minus outflow. N26 GILA RIVER PHREATOPHYTE PROJECT relation between bank-storage capacity, Sg, and of 1948-71. The shift in the rating with time reflects water-surface stage. In the first procedure, the ratio an increase in bank storage due to sediment accumu ASg/ ASg was compared to stage, where ASg and lation in the reservoir. The data were inadequate to ASg values were from the water budgets. In the define more than the two ratings shown in figure 30. second procedure, the ratio ASg/ ASy was com Much of the scatter exhibited by points from the pared to stage. ASy is the change in total storage, 1931-47 data is due to inaccuracies in the early computed in the water budget as the difference CUMULATIVE CHANGES IN SURFACE-WATER between inflow and outflow components. Relations STORAGE(A5^) AND TOTAL STORAGE (AS T), of ASg to ASft and ASg to ASy are shown in figure IN CUBICHECTOMETERS 29 for two winter budget periods. The need for 0 5 10 15 20 25 30 35 40 45 50 55 extending the time period of the water budget past the period of rapidly increasing surface-water stor age is obvious in the upper ends of the curves in figure 29A. These curves show S# and Sy decreased during April but Sg increased because of the time lag between inflow into surface-water storage and sub sequent movement into bank storage. Figure 29B is included to show the small increase in Sg , when compared to changes in Sg and Sy, in December 1967 and January 1968. This condition occurred be cause gravity drainage from bank storage was in complete at the start of the period. As a result, only the February through May period of 1968 was used in the analyses of bank storage. Figure 29 A also shows A. January through April 1965 _ that the cumulative plots of ASg versus ASg and ASy1 define the ratios ASg/ ASy and ASg/ ASg 0 5 10 20 25 30 35 40 45 50 from the slopes of lines drawn from the start to end of CUMULATIVE CHANGES IN SURFACE-WATER the period. STORAGE (ASR ) AND TOTALSTORAGE (AS r), IN THOUSANDS OF ACRE-FEET The third and principal procedure of analyzing bank storage at San Carlos Reservoir was based on CUMULATIVE CHANGE IN SU RF ACE-WATER the relation between a change in bank storage and a STORAGE (&SR ) AND TOTALSTORAGE (&ST), change in stage. The computed ASg for a budget IN CUBIC HECTOMETERS period was divided by the range in stage, giving the 0 100 200 300 400 500 600 uj 50 i i i i i i__i i i rate ASg /ft. Because each rate, ASg /ft, is related to 0 60 a specific range of stage, the rate must be associated DC with the stage which seems most representative of 0 « the budget period. A representative water-surface £ uj 40 stage is easily obtained from either of two calcula Z ° tions. The first calculation simply determines the CQ U- 40 iu H z O 30 Z O mean of the beginning and ending stages for the - c/) UJ uj Q UJ I period. In the second calculation, considered better, i< 30 the mean value of the beginning and ending surface- water storages for the period is applied to elevation 20 versus surface-water capacity tables to obtain the I- CC corresponding stage. The stage for each period is < ^a 10 -J< plotted against the corresponding ASg /ft of the D period to define the ratings of ASg and stage as D n O shown in figure 30 for San Carlos Reservoir data. 0 100 200 300 400 500 The winter stage and storage data obtained from the CUMULATIVE CHANGE IN SURFACE-WATER water budget of the reservoir and used in the above STORAGE (&SR ) AND TOTALSTORAGE (&ST), three procedures are tabulated in table 15. IN THOUSANDS OF ACRE-FEET The 1931-47 stage and storage data define one FIGURE 29. Relations of cumulative AS#to cumulative AS/? and curve of figure 30, and the other was defined by data cumulative AS#to cumulative ASyfor the periods (A) January through April 1965 and (B) December 1967 through May 1968. HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 J T27 small in comparison to water-year budget totals and COMPUTED CHANGE IN BANK STORAGE, IN for expediency was assumed zero. CUBIC HECTOMETERS PER METER The fact is stressed that reservoir water avail 0.5 2 4 681012 2510 765 ability is more than just the amount in usable surface-water storage. Figure 31 shows this differ ence by comparison of 1966 ratings of usable surface- - 760 UJ water storage capacity and total usable storage capacity. Number (66) indicates water year WATER-BUDGET ANALYSES The water budget utilizes the conservation of mass equation I-O= AS, (5) where /is inflow, O is outflow, and AS is change in storage. Identification of all the /, O, and AS com ponents included in the water budget of San Carlos Reservoir is given in equation 1. The water budget was computed by months and by water years for the 41 years of record using equat;on 1. Data for all the yearly inflow and outflow budget components except Ojgp are recorded in table 17. Analyses of computed OET data are included in the following section on evapotranspiration. Table 18 lists the storage values, ASg and ASg, the summa 2380 tion of the inflow and outflow components giver in 1 00 1 000 3000 COMPUTED CHANGE IN BANK STORAGE, table 17, and the evapotranspiration, Ogy, for each IN ACRE-FEET PER FOOT water year during the 41-year period of record. FIGURE 30. Relation between the computed change in bank- The data in tables 17 and 18 were used to compare storage capacity and elevation at San Carlos Reservoir for the magnitude of each inflow component with the water years 1931-47 and 1948-71. total inflow for the period 1931-71. The outflow com ponents were compared similarly. Gila River stream- flow contributed 78.2 percent of the total inflow; the capacity surveys. The data points for 1931 and 1932 San Carlos River, 14.5 percent; ground water, 3.5 per include an increment of water which went into cent; precipitation, 2.2 percent; and tributary flow, nonretrievable bank storage when the reservoir ini 1.6 percent. The outflow components and percent of tially filled. total outflow are: Gila River, 78.2 percent; evapo Table 16 includes usable bank storage capacity transpiration, 11.3 percent; and lake surface evap ratings for the 1931-47 and 1948-71 periods based on oration, 10.5 percent. Figure 32 compares the relat;ve figure 30. It was not practical or necessary to make magnitude of each component. an elevation-capacity rating of total bank storage because an estimate of bank dead storage would EVAPOTRANSPIRATION have been required. Water loss by evapotranspiration (ET) from the The usable bank-storage capacity at the spillway exposed surface of San Carlos Reservoir occurs by elevation of 2,511 ft (765 m) was about 152,800 acre-ft plant transpiration and by evaporation from soil, (188 hm3) for 1931-47 and about 159,200 acre-ft (196 litter, and ephemeral ponds. Water in the reservoir hm3) for 1948-71 (table 16). At this elevation, usable area becomes available for ET by movement from bank-storage capacity is about 14 percent of total streams, ground water, reservoir surface-water stor usable storage capacity. At lower reservoir eleva age, and by direct precipitation on the exposed tions, table 16 shows that usable bank storage surface. Annual ET computed by equation 1 is listed sometimes exceeds usable surface-water storage. in table 18 and plotted in figure 33. Sg is never static because of the time of response Large errors in the computed .ETlosses occur when required to adjust to changes in Sg. However, the one or more of the hydrologic components of the quantity of water required to place SB and S# in reservoir are in a state of rapid transition at the end equilibrium at the end of a water year is usually of a budget period. The annual ET shown in figure 33 N28 GILA RIVER PHREATOPHYTE PROJECT TABLE 15. Results of procedures to determine bank storage capacity at San Carlos Reservoir Startir AS/ A% ASB end igngan<1 Mean Mean Elevation of ^ ^ ^ Water Period eleva tions elevation Sp mean S/j year included (acre-ft) (acre-ft) (acre-ft) (ft) (ft) (acre-ft) (ft) AS T AS R ft 949 1931 ... . Nov.-Mar. 92,277 71,812 20,465 f" L76 2428.71 163,059 2429.20 0.222 0.285 1,472 3.66 94^ 1932 . . ... Dec.-Apr. 323,063 270,007 53,056 7~ 2454.31 338,814 2456.68 .164 .196 1,600 J.JH) 240 1935 ... .. Dec.-Apr. 136,282 121,428 14,854 ;," 7 2422.03 122,006 2424.65 .109 .122 520 24o 3.ol 1936 . Jan.-Apr. 88,530 71,804 16,726 ^ ^ 2427.52 137,102 2428.15 .189 .233 1,118 i4o oqn ' 7ft 1937 ...... Jan.-Apr. 264,946 239,274 25,672 ~~ ° 2424.12 153,975 2431.80 .097 .107 487 i4o 3.46 OOQ 1939 ...... Nov.-Apr. 22,826 18,513 4,313 ^° !';f 2390.18 19,935 2390.86 .189 .233 355 £,A\J 3.26 OOQ 1940 .. . Jan.-Mar. 49,777 40,906 8,871 ° 7'^ 2397.95 35,185 2400.03 .178 .217 444 246 t 09 1941 ...... Mar.-June 359,660 312,877 46,783 ''"2 2481.00 578,220 2482.04 .130 .150 1,811 948 3 QA 1942 ...... Sept.-Mar. 215,359 190,272 25,087 ^ " 2495.39 753,257 2495.24 .116 .132 1,903 ioO ..JO OOQ R7 1946 ...... Jan.-Feb. 17,718 14,577 3,141 ~^ j.oy'°' 2396.23 21,236 2396.69 .177 .215 360 OOQ 3 AO 1948 ...... Jan.-Apr. 18,858 12,962 5,896 ~° _T~ 2389.18 10,521 2390.08 .313 .455 479 io9 Xoo OOQ 3 1 ft 1949 ...... Dec.-Apr. 312,140 251,306 60,834 ~? '*° 2416.94 129,452 2430.58 .195 .242 901 245 oqo D 00 1952 ...... Dec.-Mar. 196,070 155,216 40,854 ^43 ;: 2409.94 80,936 2420.16 .208 .263 768 3.55 OOQ 1953 ...... Jan.-Mar. 14,686 10,544 4,142 x53 2390.59 9,690 2391.44 .282 .393 409 239 5.65 OOQ 1 10 1954 ...... Mar. 51,082 36,336 14,746 ^4° .,:. 2395.34 21,043 2394.74 .289 .406 607 .oO OOQ ~) CA 1957 ...... Jan.-Feb. 11,715 7,422 4,293 f** : " 2387.68 5,795 2389.00 .366 .578 414 £iA\J i.OO 941 J04 1958 ...... Feb.-Apr. 204,404 167,062 37,342 ^ ' 2430.17 133,899 2433.59 .183 .224 1,090 J f)0 1960 ...... Nov.-Mar. 196,941 163,768 33,173 ^44 :'"^ 2426.64 117,198 2430.93 .168 .203 891 >.^o OOQ ? 17 1962 ...... Nov.-Apr. 181,480 141,049 40,431 ~* '' 2414.70 77,624 2421.96 .223 .287 897 i4o 9QQ i f>7 1963 ...... Oct.-Dec. 39,560 30,557 9,003 !~ ^' 2405.42 29,343 2406.40 .228 .295 657 240 7 47 1965 ...... Jan.-Apr. 39,904 31,521 8,383 * '' 2412.99 45,550 2413.46 .210 .266 799 s.ol OOQ j 17 1966 ...... Nov.-May 520,735 414,683 106,052 "7 ,' ' 2430.24 210,140 2448.77 .204 .256 1,260 L.A£I T ffi 1968 ...... Feb.-May 320,492 279,289 41,203 ^49 j^ 2478.15 488,088 2479.03 .129 .148 1,700 for 1941 is an example of this condition. This error is area available for ETloss is 20,850 acres (8,438 hm2), compensated, however, by an error of equal magni less the lake surface area. tude but of opposite sign during the following year(s) Surface conditions on the exposed area rrnged and is of no significance in the 41 -year mean annual from open bodies of shallow water to dense phreato- ET rate. phytes and from wet to very dry soil. Optimum Determination of the size of the "exposed surface surface conditions for high ET exist over a large area of the reservoir" is a prerequisite to computing reservoir area following a major lake stage recession the ET by depth. The reservoir area at 2,525 ft (770 m) such as occurred in 1942-45. is 19,925 acres (8,064 hm2). This area excludes ap The computed volume of monthly ET was divided proximately 60 acres (24 hm2) which lie within the by the mean monthly exposed area providing a value reservoir boundary but are upstream from the Gila of monthly ET depth. Water year totals of these River Calva station. Added to the reservoir area, monthly ET depths are listed in table 19 and are however, are 925 acres (374 hm2) in the San Carlos plotted in figure 34. The computed mean annual River flood plain between the Peridot gaging station depth of ET was 1.47 ft (0.448 m). and the reservoir boundary, giving a total of 20,850 For each month, 41 values of .ETdepths were avail acres (8,438 hm2) as the maximum area possible for able from the water budget. All monthly values were ET loss. At any specific time, the exposed surface used to indicate the most common range in FT for HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N29 TABLE 16. San Carlos Reservoir elevation-capacity tables of usable bank storage, usable surface-water storage, and total usable storage Period 1931-47 Period 1948-71 Cumulative usable storage, in acre-ft Cumulative usable storage, in acre-ft Elevation Bank Surface water Total Bank Surface water Total (ft) SB SR ST SB SR ST 2382.631 ...... 0 2 0 0 0 3 o 0 2385 ...... 770 1,735 2,505 1,006 660 l,66f 2390 ...... 2,520 6,668 9,188 3,269 2,845 6,114 2395 ...... 4,483 13,249 17,732 5,769 6,728 12,497 2400 ...... 6,670 22,041 28,711 8,531 12,865 21,39f 2405 ...... 9,095 33,468 42,563 11,581 21,749 33,330 2410 ...... 11,795 46,941 58,736 14,931 33,308 48,23? 2415 ...... 14,820 62,474 77,294 18,581 47,343 65,924 2420 ...... 18,185 80,102 98,287 22,531 63,284 85,815 2425 ...... 21,945 100,411 122,356 26,806 81,217 108,02" 2430 ...... 26,095 124,115 150,210 31,431 102,202 133,63? 2435 ...... 30,670 150,760 181,430 36,431 126,269 162,700 2440 ...... 35,720 180,020 215,740 41,831 153,572 195,403 2445 ...... 41,270 212,197 253,467 47,606 184,059 231,665 2450 ...... 47,295 247,463 294,758 53,706 217,811 271,517 2455 ...... 53,720 285,832 339,552 60,131 254,977 315, IOF 2460 ...... 60,495 327,993 388,488 66,906 295,976 362,882 2465 ...... 67,620 374,278 441,898 74,031 341,707 415.73F 2470 ...... 75,120 424,606 499,726 81,531 392,073 473,604 2475 ...... 83,020 478,736 561,756 89,431 445,822 535,25? 2480 ...... 91,320 536,141 627,461 97,731 502,827 600,55F 2485 ...... 100,020 597,432 697,452 106,431 503,363 669,794 2490 ...... 109,145 662,965 772,110 115,556 627,710 743,266 2495 ...... 118,720 732,575 851,295 125,131 696,272 821,40? 2500 ...... 128,770 806,491 935,261 135,181 770,200 905,381 2505 ...... 139,345 884,898 1,024,243 145,756 848,607 994,363 2510 ...... 150,470 967,746 1,118,216 156,881 931,456 1,088,337 2511 ...... 152,750 984,874 1,137,624 159,161 948,584 1,107,745 2515 ...... 162,170 1,055,286 1,217,456 168,581 1,018,996 1,187,577 'Elevation of zero usable storage. 2From 1947 tables of usable surface storage. ^From 1966 tables of usable surface storage. CAPACITY, IN CUBIC HECTOMETERS range of the central two-thirds of the values for each 200 400 600 800 1000 1200 1400 month is bracketed. This approximately corresponds 2520 to the number of values included in one standard (From 1966 Capacity Survey) 2510 - 765 deviation. The seven values above and seven b?low 2500 the bracketed range were plotted for each month. The -760 < monthly medians have also been identified in figure 2490 Usable surface-water, storage capacity 35. The occurrences of extreme values of computed 2480 755 ET usually coincide with periods of vigorous change 2470 in one or more water-budget components. An un 2460 750 realistic extreme resulted when bank storage had not adjusted to the change in stage, although changes in 2450 745 lake stage and changes in bank storage wero as 2440 sumed simultaneous in water-budget computations. 2430 740 The mean annual ET of the monthly mediars in 2420 figure 35 is 1.45 ft (0.442 m). This value corresponds Shaded area equals usable to the mean of the annual ET values in figure 34, - 735 2410 bank-storage capacity computed as 1.47 ft (0.448 m). 2400 The seasonal trend ofETis obvious in figure 35 in - 730 2390 spite of the large scatter exhibited. After excluding 2380 extreme values (outliers) the data were examined for 1 2 3 4 5 6 7 8 9 10 11 12 possible changes in rates over the life of the resei*voir CAPACITY, IN 100,000 ACRE-FEET and for obtaining more realistic values of mean monthly ET depths. The monthly data were sepa FIGURE 31. Elevation-capacity relations for usable surface- rated into 4 periods of 10 years each, beginning with water storage, usable bank storage, and total usable storage 1931. Within a 10-year period, the maximum and in 1966, for San Carlos Reservoir. minimum extremes were omitted from the 10 values each month, to show the monthly extremes, and to for each month, and a mean monthly ET was illustrate the seasonal ET trend. In figure 35, the obtained from the 8 remaining values. Figure 36 N30 GILA RIVER PHREATOPHYTE PROJECT TABLE 17. Summations of San Carlos Reservoir inflow-outflow components by water year, 1931-71 Inflows for year in acre-ft Outflows for year in acre-ft Gila San Carlos Gila To'al Water year River River Precipitation Ground water Tributary Total inflow River Evaporation outflow1 1931 ...... 289,917 36,677 5,850 7,994 3,580 344,018 223,920 23,008 246,928 1932 ...... 442,175 51,950 9,565 8,015 1,760 513,465 256,150 44,455 300,605 1933 ...... 149,072 16,802 7,399 7,994 2,460 183,727 334,910 36,244 371,154 1934 ...... 160,085 13,733 1,895 7,994 2,660 186,368 184,660 15,416 200,076 1935 ...... 149,423 87,670 6,684 7,994 4,020 255,791 184,553 21,554 206,107 1936 ...... 150,165 44,559 3,659 8,015 1,760 208,157 228,090 22,162 250,252 1937 ...... 317,944 46,630 3,717 7,994 1,760 378,046 279,621 29,436 309,057 1938 ...... 106,170 15,713 2,505 7,994 1,760 134,142 189,720 14,321 204,041 1939 ...... 91,500 18,378 1,362 7,994 1,760 120,994 102,426 9,365 111,791 1940 ...... 158,275 15,858 1,891 8,015 1,760 185,799 160,720 10,323 171,043 1941 ...... 803,991 201,192 22,378 7,994 6,990 1,042,546 215,724 54,381 270,105 1942 ...... 314,222 25,273 16,250 7,994 2,410 366,150 352,030 74,465 426,495 1943 ...... 102,531 30,191 10,954 7,994 2,200 153,870 365,140 60,302 425,442 1944 ...... 80,725 13,161 7,512 8,015 6,070 115,483 297,430 34,186 331,616 1945 ...... 131,705 17,038 3,863 7,994 3,010 163,610 216,290 20,734 237,024 1946 ...... 55,627 15,233 1,245 7,994 4,850 84,949 74,550 7,049 81,599 1947 ...... 45,607 11,141 796 7,994 3,550 69,088 59,983 5,467 65,450 1948 ...... 63,511 10,390 620 8,015 2,530 85,066 68,270 5,913 74.183 1949 ...... 422,114 23,192 3,863 7,994 2,680 459,843 254,061 29,914 283.975 1950 ...... 37,441 5,908 2,709 7,994 2,530 56,583 148,860 13,692 162.552 1951 ...... 35,304 9,134 808 7,994 2,930 56,170 36,347 4,866 41.213 1952 ...... 191,624 80,840 4,658 8,015 2,620 287,758 229,435 22,710 252 145 1953 ...... 42,937 8,384 861 7,994 1,760 61,936 49,319 5,983 55.302 1954 ...... 116,372 42,254 2,345 7,994 7,430 176,396 68,964 10,579 79,543 1955 ...... 123,593 26,899 3,194 7,994 6,960 168,639 97,710 12,342 110,052 1956 ...... 20,858 13,886 2,053 8,015 1,760 46,572 109,062 12,572 121.634 1957 ...... 128,264 9,136 586 7,994 1,760 147,740 52,123 5,288 57,411 1958 ...... 296,372 47,883 5,676 7,994 6,420 364,345 243,220 28,118 271.338 1959 ...... 97,574 6,419 2,290 7,994 5,920 120,197 147,870 15,965 163 835 1960 ...... 193,693 64,990 3,809 8,015 3,940 274,447 256,896 26,884 283 780 1961 ...... 45,499 6,189 461 7,994 5,080 65,223 25,312 2,449 27,761 1962 ...... 275,405 33,567 2,650 7,994 2,980 322,596 246,730 21,971 268 701 1963 ...... 175,069 34,123 3,340 7,994 3,580 224,106 141,430 18,074 159 504 1964 ...... 94,351 10,301 1,697 8,015 7,620 121,984 107,170 12,697 119867 1965 ...... 90,948 24,550 2,803 7,994 1,940 128,234 121,999 13,688 135 687 1966 ...... 533,205 119,391 13,948 7,994 8,580 683,118 226,476 53,587 280063 1967 ...... 148,375 11,295 7,697 7,994 5,800 181,162 255,250 44,067 299,317 1968 ...... 579,171 72,822 12,339 8,015 1,760 674,107 281,340 70,871 352.211 1969 ...... 60,545 15,599 11,171 7,994 2,480 97,789 315,376 59,744 375 120 1970 ...... 31,214 12,502 5,889 7,994 3,560 61,159 218,860 28,413 247,273 1971 ...... 59,775 19,247 861 7,994 3,920 91,786 57,463 5,777 63240 1931-71 totals . 7,412,348 1,370,100 203,853 327,964 148,890 9,463,160 7,485,460 1,009,032 8,494.492 'Does not include evapotranspiration losses. shows the resulting monthly means for each 10-year August .ET was often underestimated and September period. The seasonal trend is apparent for all four ET overestimated. periods, but no obvious changes in ET rates can be Vegetation increased on the exposed areas cf the detected during the life of the reservoir. reservoir flood plain, especially following the 1941- The average of the annual mean ET values com 42 floods (Turner, 1974, fig. 4). If an increasing trend puted from these four periods is 1.51 ft (0.460 m), in ET could have been conclusively shown, chs nges which is slightly higher than that obtained when the in ET would have been correlated with the increase maximum and minimum extremes are included in in vegetation. Data used in figure 34 were examined the computation. The monthly mean and median ET for an indication of increased ET, since no increasing values and the water-year means from the data trend was evident in figure 36. Mean annual ET was shown in figures 35 and 36 are listed in table 20. computed for the selected periods shown in figure 34. Two characteristics can be noted about the sea Only those periods of least stage change were used, sonal trends in the computed ET values shown in thereby eliminating periods when soil-moisture con figures 35 and 36. First, the computed ET is essen tent was high over large areas. Thus, a greate^ per tially zero during the winter months from December centage of the total ET should have been through through February in part because zero ET was used transpiration and not by evaporation from exposed in the development of the bank-storage ratings. areas of bare ground. Mean annual ET depths were Second, the reservoir surface-water storage normally computed as 0.93 ft (0.28 m) from 1934 to 1940,1.07 ft increases during August, and the bank storage (0.33 m) from 1945 to 1957, and 1.48 ft (0.45 m) from response to this increase does not approach equi 1959 to 1965. This shows an apparent increase in ET, librium until sometime in September. As a result, but as figure 34 indicates, the range in arnual HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N31 Precipitation 2.2 percent^ /Tributary flow 1.6 percent were too greatly affected by the large fluctuations Ground water 3.5 percent in lake stage from 1966 to 1971. Although precipitation falling on the exposed a rea of the reservoir is a reservoir inflow, a distinction is made between the relation of this inflow to ET and the relation of inflow from other sources to ET. The ET loss computed by the water budget (table 18) represents a loss in usable reservoir water. Normal ly, only a minimal amount of the input from direct precipitation on the exposed areas is ever a par4 of "usable" contents. The fact that precipitatior is distributed on the surface enhances the possibility for immediate and total ET. Vaporization of the precipitation depletes the energy available for vapor izing water from other sources, but this effect is INFLOW temporary in arid regions because of the infrequent and limited quantity of precipitation. All precipitation on the exposed ground area of the Evaporation 10.5 percent reservoir is an additional .ETloss. This added ETis assumed equal to precipitation measured at the Pan Carlos Reservoir weather station. ET from this Evapotransp [ration precipitation source was added to the ET computed 1 1.3 percent from the water budget of the reservoir (table 18) to give the total ET from the reservoir water-surface area and adjacent exposed ground area. The average annual total ETfor the 1931-71 period is 2.62 ft (C .80 m). A comparison of this value with the computed water-budget ET values in table 20 indicates that precipitation on the exposed area of the reservoir contributed an average of about 1.2 ft (0.37 m) per year to the total ET. OUTFLOW DEVELOPMENT OF SURFACE-WATER FIGURE 32. Relative magnitude of inflow and outflow water- STORAGE-CAPACITY RATINGS budget components. SIMULATION OF THE SEDIMENT DEPOSITIONAL PROCT.SS Interpolations of capacity changes between capac amounts during each period is too great to state ity surveys were made by using a procedure which definitely that the increase is related to vegetation included simulating the sediment depositional changes. process in the San Carlos Reservoir. The simulation The total exposed surface area of the reservoir I procedure was structured about three basic phases of extends outside the flood plain because much of this the depositional process: surface area was occasionally inundated. Generally, 1. Sediment inflow however, the highest rates of ET are from the flood- 2. Sediment distribution plain portion of the area. Use of the total exposed 3. Sediment compaction surface area prevented making a more accurate Equations were developed to represent each phrse. evaluation of vegetative ET losses. The "best fit" values of variables in the equations Flood-plain vegetation in the reservoir area was were selected by minimizing the difference between removed beginning in the 1967 water year. A com the volumes of sediment measured and estimatei. parison of monthly before-clearing and after- Measurements of sediment accumulation were clearing data was made for periods 1961-66 and available from only four separate periods between 1967-71 to evaluate vegetative consumptive use 1929 and 1966. However, volumes of sediment depos (transpiration). The results of these comparisons ited within 5-foot-elevation increments were defined were inconclusive, however, because the ET rates from each survey, and these volumes provided the N32 GILA RIVER PHREATOPHYTE PROJECT TABLE 18. Water-budget summations Water-surface Surface-water Surface-water Change in Evaio- elevation storage storage change Bank storage bank storage Inflow Outflow1 transpiration- Water year (ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) (acre-ft) 2424.40 139,361 ' 1931 2430.66 163,401 -24,040 "5'204 344,018 246,928 67,846 -146,313 -25,132 513,467 300,605 41,417 932 2453.53 309,714 199,083 33'441 183,727 371,154 45,077 |£ 2420.26 110,631 asqn 36,984 5'476 186,368 200,076 28,751 |934 2411.85 73,647 \oq\4 -34,803 ~6'616 255,791 206,107 8,236 J93^ 2421.78 108,450 \qvtn 63,470 11,647 208,158 250,252 33,024 9* 2402.50 44,980 77000'8_T 1937 2418Q4 9121Q -46,230 ~8'989 378,046 309,057 13,739 ®q 75,072 14,961 134,142 204,041 20,134 *° 2388.26 16,138 -327 ~357 120,994 111,791 940 -- -- 2389.28 16,465 2268 8,519 5,189 ' 980 185,800 171,043 20,926 i»w 2386.48 11,276 1941 ...... 2491.64 696,666 -685,390 112286 -110,998 1,042,546 270,105 -23,947 102,486 ' 14'023 366,150 426,495 56.1S4 194^ 2483.99 594,180 194d ...... 2459.22 329,562 264,618 38'825 153,870 425,442 31,871 944 ------2424.70 105,620 223,942 37'718 115,484 331,616 45,528 1945 2399.67 26,578 79,042 15' 194 163,610 237,024 20,822 1946 ...... 2393.68 15,211 11,367 2,561 84,949 81,599 17,278 15,0?7 1947 2386.02 6,260 8,951 2,497 69,088 65,450 948 ...... 2382?5 3j542 2,718 1,384 85,067 74,183 14,9?<5 -105,910 -28,360 459,843 283,975 41,598 iq^n 2426.77 109,452 00449 1950 ...... 2383.36 3,694 105,798 28'109 56'583 162,552 27,898 1951 2382.81 3,060 634 226 56,170 41,213 15,8' 7 1952 ...... 2384-.00 3,499 -439 -488 287,759 252,145 34,6^7 1953 2382.57 2,581 918 586 61,936 55,302 8,138 9^4 ------2414.91 59,024 -56,443 -18,506 176,396 79,543 21,904 1955 2421.74 81,836 -22,812 94 nw ~5'503 168,639 110,052 30,272 I95b ...... 2382.30 2,004 79,832 '*"*iM 24' 120 46'573 121,634 28,891 957 ...... 241556 5gln -56,107 -19,124 147,740 57,411 15,098 1900 ...... 2426.49 97,988 -39.877 ~9'161 364,345 271,338 43,970 28184 ' 1959 ...... 24Q6 5Q gl 53g 66,450 15,598 120,197 163,835 '~" 38,410 itwu ...... 2382.89 1,830 29,708 12,445 274,448 283,780 32,821 9bl ...... 239651 n92() -10,090 -6,462 65,223 27,761 20,910 -2,144 _ -1,138 322,596 268,701 50,613 u«w 2398.57 14,064 18W ...... 2415 lg 51)66() -37,596 ' -10,962 224,106 159,504 16,024 I»M ...... 2408.87 33,078 18,582 4'549 121,985 119,867 25,250 19b5 23911? 446g 28,609 10'320 128,234 135,687 31,476 -312,260 -66,230 683,118 280,063 24,565 i»DD 2462.23 316,729 in'"" (tot4 19b7 2447n 19573g 120.990 19,904 181,162 299,317 22,738 I9ba ...... 2477.86 471,372 -275,633 04170 -43,998 674,108 352,211 2,235 I9b9 ...... 2448g2 2Q5212 266,160 ' 41'912 97'789 375,120 30,741 .', .... 24Q4 54 2Q 7gl 184,431 40'966 61,159 247,273 39,2^3 ...... 2412.27______37,542 -16,761 -5.288 91,786 63,240 6,4:98 Ib.ooo,oo 'Does not include evapotranspiration losses. 2Excludes precipitation from exposed area of reservoir. increment is considered a separate surface-vater storage reservoir. The sediment inflow phase of the simulation pro cedure provided estimates of weight of incoming sediment by assuming that sediment inflow is a function of streamflow. The limitation of this as sumption is the large range of sediment concentra tions which occur for any given water discharge. However, for long time periods it is assumed that use UJH of mean sediment concentrations is acceptable, if adjustments are made for seasonal differences in concentration. According to the U.S. Army Corps of Engineers WATER YEAR (1914, par. 92, p. 30), the total sediment discharge in summer averaged about 2.5 percent, by weight, of the FIGURE 33. Annual evapotranspiration from exposed area of discharge of the water-sediment mixture. In winter, reservoir computed by reservoir water budget. the ratio of discharges was approximately 0.5 per basis for developing and testing the simulation of the cent, so the summer-to-winter concentration ratio sediment depositional process. In the simulation, was about 5:1. Burkham (1972, p. 8) derived a similar each storage unit identified by a 5-foot-elevation ratio based on 1965-70 U.S. Geological Survey data HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N33 TABLE 19. Total evapotranspiration (al) for ban Carlos Reser 1 1 1 1 1 1 1 1 1 1 voir, by water year °4.4 °1.7 1.2° o 1.4 1.0 - 0.30 ET from precipitation ET as residual of exposed 0.9 of water budget reservoir surface Total ET - 0.25 Water year (ft) (ft) (ft) 0.8 1931 ...... 3.55 1.30 4.85 0.7 1932 ..... 3.18 1.18 4.36 ° Q 8 - 0.20 oo 1933 . ... 2.88 1.12 4.00 DC 1934 . .. 1.08 .54 1.62 h 0.6 LU LU h- 1935 ...... 20 1.64 1.84 LU LU 1936 ...... 1.81 .97 2.78 " 0.5 - 0.15 % 1937 ...... 86 1.08 1.94 z Z ...... 97 .98 1.95 . 0.4 - 3 ' 2 A j'2 8- .29 .89 1.18 -0.10 § 1940 ...... 93 1.04 1.97 | 03 1941 -3.08 2.54 -.54 1942 .... 7.86 1.08 8.94 8 g o 2 t h 1943 ...... 2.95 .98 3.93 DC 0.2 - o.or cc CL 1944 2.71 1.25 3.96 0. 1945 ...... 97 1.13 2.10 jjj 0.1 00 1946 ...... 58 .96 1.54 "I ^ fT "1~\ " i; +2 -i | | { 3± 212 £2 \ 24- 1947 DC 0 - 0 < DC 1948 ...... 61 .77 1.38 ! s I ]_ I 1 g 2° t 2 1- 1949 ...... 2.41 1.14 3.55 2-o.i o 1950 ...... 1.42 .93 2.35 - -0.05 < 1951 . .63 .99 1.62 > -0.2 1952 .... 1.86 1.55 3.41 LU 1953 .... .31 .90 1.21 .66 1.60 2.26 -0.3 - -0.10 1955 .... 1.20 1.17 2.37 1956 ...... 1.48 .75 2.23 -0.4 1957 ...... 61 .93 1.54 - -0.15 1958 ..... 2.25 1.66 3.91 -0.5 1959 ...... 1.78 .98 2.76 -0.9 1960 ...... 1.66 1.28 2.94 -0.6 1961 ...... 75 .92 1.67 1962 ...... 2.69 1.11 3.80 -5.0 r 1.52 1963 ...... 62 1.24 1.86 1964 . .. .91 1.08 1.99 1965 ...... 1.54 1.17 2.71 1966 ...... 2.31 2.26 4.57 MONTH ~" W 1967 .... 1.13 1.11 2.24 EXPLANATION 1968 . . .37 1.38 1.75 i ! 4 1969 ...... 2.48 1.12 3.60 -?- Number indicates actual evapotranspiration, in feet 1970 ... 2.21 1.11 3.32 Range of 2/3 of monthly values .05 .74 .79 1971 .. . + Median of monthly values -L Monthly values outside bracketed range Ml M M M M M \ M ' M 1 1 i M M 1 1 1 M M ' | 00 2 Number indicates number of values I * J*CO0)MOlvj0 EXPLANATION 2.0 £ FIGURB: 35. Computed monthly evapotranspiration at Fan PIRATION,INFEET , ___, - LU Carlos Reservoir for water years 1931-71. Mean annual ET depth -- 1.5 5^ for period bracketed 2 0.4 -0.12 z O -0.10 ° \( .-1.0 I P 0.3 - 0.08 < - o.oe o: \ A \ A A ,,/WUA /Y°-5 \ Q- LU _ _ f Q- m 00 1 - 0.04 oo j_ Z i _ o (/)2 < 0 - - 0.02 <^ DC H~ ° ^^^ - 0.00 £ 2 * -0.02O" EVAPOT -" ~~°'5 o O i iCO10_ Q- -0.1 1 °- -0.0'' < 1 -1.0 < Lu -0.2 - -0.0~LU III «- o o o o«- co ^ in co r^r^ 0) 0) 0) O) 0)0) MONTH WATER YEAR EXPLANATION ...... 1931-40 FIGURE 34. Annual depth of evapotranspiration from the 1 JH- 1 3U exposed surface of San Carlos Reservoir for water years 1931-71. 1OR 1 ~rn of suspended sediment for the Gila River station at FIGURE 36. Mean monthly evapotranspiration depths computed the head of Safford Valley, which is located about 50 for 10-year periods. mi (80 km) upstream from San Carlos Reservoir. The the reservoir is not known, nor is it known how the change in this ratio from the Safford Valley site to ratio would be affected by using total sediment N34 GILA RIVER PHREATOPHYTE PROJECT TABLE 20. Mean monthly euapotranspiration (ET) computed from 4 periods of 10 years each, and median monthly evapotransp'.ration for 41 years Computed monthly ET (ft) Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Annual Mean monthly from 4 periods of 10 years each ...... 0.123 0.092 -0.009 0.003 0.004 0.062 0.168 0.212 0.274 0.239 0.166 0.176 1.510 Median of 41 monthly values ...... 109 .071 .044 - .018 .005 .099 .142 .193 .300 .198 .155 .150 1.448 discharge instead of solely the suspended sediment both are constant during each trial of the simulation discharge. Estimates of the magnitude of deposition which compares the estimated with the measured in San Carlos Reservoir were made with ratios of sediment deposition. Equation 9 was modified for summer-to-winter concentrations in the range of 1:1 these assigned values, and the resulting equation to 10:1 for the four periods prior to implementing the provided estimates, designated Sy, which were pro total simulation procedure. Comparison between portional to Si- The modified equation is estimates and measurements of deposition showed sy = +0 that results using the suggested 5:1 concentration w (10) ratio were only slightly better than those using a 1:1 Each daily streamflow amount was assigned to ratio. the 5-foot-elevation increment (incremental storage A general equation relating the weight of sediment reservoir) into which streamflow occurred; the proper discharged by a stream to the stream inflow volume incremental reservoir was determined by the lake during a fixed time interval is stage at the end of the day. Daily streamflow data was summed according to water year, season of the S=CQ , (6) year, and incremental reservoir. The proportional where Sis the weight of sediment discharged, Cisthe sediment weight, Sy, for each year and each incre mean sediment concentration expressed as the mental storage reservoir was computed by inserting weight of sediment per unit volume of inflow, and Q the appropriate Qs and Q^ sums into equation 10. is the volume of stream inflow. The weight of se.di- Table 21 shows a generalized chart of Sy- into a ment retained by the reservoir, Sj, is equal to S times reservoir, where i = I to n designates the increir^mtal the trap efficiency, E. The weight of trapped sedi storage reservoirs and j - 1 to m designates the water ment is therefore years. In table 21, the proportional sediment weight for When equation 7 is expanded to include seasonal any given year is determined by summing the Syj ; terms for C and Q, it becomes values in the column corresponding to that year. Similarly, a summation of Syj values for a partic ular row of the table is the proportional sediment where Cw and Cs are the mean winter and summer weight for an elevation-increment of storage. The sediment concentrations, respectively, and Qw and total Sy for a period is therefore Qs are the winter and summer streamflow summa tions, respectively. The ratio r, where r = CS/CW, was one of the variables for which an optimum value was sought in TABLE 21. Chart of notation used to identify time and inflow defining the sediment deposition equations. Substi location of computed proportional sediment weights, £ -,- tuting r into equation 8 gives Water year, j 1 2 m -1 m which eliminates Cs from the equation. A value of r sn,i syi,2 * * s-vi, m -i syi,m Incrementalstorage 3 to1i-" was assumed for the initial trial through the simula reservoir,i tion procedure. The value of r was adjusted in subse quent trials to improve the results from the simula-' 3 s s s s tion procedure. vn-l,l yn -1,2 vn-l, m-l >'n-l, m E and Cw were assigned values of unity because s»u syn,2 " * syn,m-i syn,m HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N35 n m 2 s: (ID The second phase in the sediment depositional Suspended sediment deposited process is the distribution of sediment inflow within in reservoir a reservoir. As a stream merges with pooled reservoir water, water velocities decrease, resulting in deposi FIGURE 37. Sketch identifying terms used in simulation of tion of sediment. suspended sediment distribution. In this preliminary simulation the reservoir is assumed uniform in width and bottom configura The optimum values for the distance DA and the dis tion. Another assumption is that the larger sediment tribution exponent x were found in the procedure particles are deposited immediately upon entry into which selected best estimates of sediment deposition. the surface-water storage pool of the reservoir. To simulate distribution of suspended sediment The weight of larger sediment particles to the total into incremental reservoirs, DA and DB of equa sediment weight was defined as a. Selection of an tion 13 were redesignated DAI and DB^ respec optimum a was done in the simulation procedure by tively. The subscript i represents the incremental comparing estimated with measured sediment depo reservoir into which sediment entered the reservoir sition. The Syij values were divided into two parts by pool, and k represents the incremental reservoir for use of the equation which deposition is being computed. Point A is the upstream limit of reservoir i, and point B is the up Sy =aSy +(1.0-a)Sy. (12) stream limit of reservoir k. Syj is the computed The quantity (1.0 - a)Sy is the part of Sy made up of quantity proportional to sediment weight entering the smaller (suspended) sediment particles. Some of incremental reservoir i at point A, so the suspended this quantity of smaller particles is assumed to be sediment fraction of Sy - is Ss -, The suspended sedi deposited within the incremental storage reservoir ment which passes into reservoir k at point B is con where the stream enters the storage pool, and the remainder is assumed to move to lower incremental g x reservoirs and is then deposited. sequently computed as *'(%) ' The sediment The computed weight of smaller particles, (1.0 - a)Sy, was designated S§ to reduce equation symbol passing into the next lower incremental reserved, ism. Ss was exponentially distributed over the dis D x tance from the point of inflow to a point where depo Bk+l k + 1, is sition is considered complete. Referring to figure 37, The difference between the deposition of suspended sediment was distri ) buted from point A, the point of inflow, to point C, these two amounts, Ss^ .is proportional to the sus over the distance DA. Bis a point along DA, and DB pended sediment weight deposited in incremental is the distance from point B to point C. The ratio of reservoir k and is given as the weight of suspended sediment passing point B to U Z> v jr~ \ , where x is the r __. __ ___. ( A/ In the simulation procedure, the proportional weight of suspended sediment passing B is equal to The S§i total for each incremental reservoir was FJ 00 / L* ID v distributed by SSfc amounts into the appropriate Ss | TT~ I. The difference between quantities pass- (/)\ DA/ incremental reservoirs by equation 14. Distribution of Ssi started with k-\ and continued through suc ing A and B is the proportional weight of suspended sediment deposited between A and B, designated cessively lower incremental reservoirs to either the SS r>. Accordingly, lowest incremental reservoir or to the end of DA^ (at point C ), whichever came first. Incremental reser voirs were numbered from 1, for the upper, reservoir, SB (13) to n, for the lowest, and SSj was distributed into all incremental reservoirs from i = 1 to i = n. N36 GILA RIVER PHREATOPHYTE PROJECT If the optimal value selected for D^- was greater than the distance from point A to the dam, a part of Distance from inflow point to dam the SSj quantity could not be distributed by equation 14. This remaining quantity was distributed uni formly over the distance from point A to the dam as istribution of sediment shown in figure 38. by equation 14 For San Carlos Reservoir, distribution was made " Uniform distribution of remaining by water year. Thus, within each of the four periods, sediment after distribution of the deposition was categorized by the incremental first part by equation 14 storage reservoir of deposition and by water year. FIGURE 38. Sketch showing distribution of suspended sediment, For incremental reservoir k and for any water year j, Ss ., when distance DA was computed as greater than the dis designation of the computed amount deposited tance from inflow point (A) to the dam. was The simulating process continues with the com measured deposition was established for each period paction phase after the sediment is distributed and by the following equation: deposited. Lane and Koelzer (1943) presented a com paction equation to estimate unit weight -of sedi SM=RATIO (16) ments at a specified time following deposition. This where SM is the total volume of sediment deposited equation requires knowing the "in place" composi in the period. RATIO is a proportionality constant tion of the sediment and its specific weight 1 year whose value is affected by E and Cw of equation 9, after deposition. This information was unavailable which had been set equal to unity for the computa for San Carlos Reservoir. However, the Lane and tion procedure. RATIO also includes a unit conver Koelzer equation was applied to the reservoir using sion to relate the measured volume of SM to SR. Each estimates of percentages of sand, silt, and clay repetition of the simulation produced a different deposited after 1 year and an estimate of the specific value for RATIO. weight of the deposit. The amount of compaction esti The estimate of absolute volume of deposited mated by this method was found to be small com sediment, Sej^, was made for each 5-foot incremental pared to the probable error in the simulation of sedi reservoir by multiplying the periods RATIO times ment deposition. Also, the addition of a compaction the SRfc of the incremental reservoir: equation to the simulation procedure resulted in un acceptable parameter values in the sediment inflow Sek =RATIO (SRk). (17) and distribution equations. For these reasons, the The value of one or more of the variables, r, a, x, or compaction of reservoir sediments was deleted from DA, was changed slightly for each trial of the further computations. simulation procedure. The optimum values of vari With deletion of the compaction phase from the ables were naturally those which produced the best simulation, the results of only the sediment inflow sediment estimates. A listing of the variables and and sediment distribution phases were used in mak optimum values are shown in table 22 for the four ing estimates of sediment deposited. The computed periods between capacity surveys and for the 1929- proportional weights for distributed sediments the 66 period. amounts were summed for each incremental reservoir and for each of the periods including the TABLE 22. Optimum values of variables from simulation of the 1929-66 period. The incremental reservoir sums are sediment depositional procedure Variables designated SR^ , and the total SR^ amount of a Period number and dates r a X *>A period is SR. SR can be expressed as No. 1, 1929-35 ...... 13.20 0.25 1.30 60000ft n m No. 2, 1935-37 ...... 1.80 .40 .88 40 000 ft No. 3, 1937-47 ...... 2.35 .38 .82 72 000 ft SR = No. 4, 1947-66 ...... 1.35 .55 .82 16 000 ft <<-*y ±-iT (15) No. 5, 1929-66 ...... 4.65 .35 1.60 56 000 ft k = lj=l Symbols: r is the seasonal ratio of summer to winter sediment concentration. a is the percent, by weight, of total sediment load deposited when streamflow where the range of incremental reservoirs is from k=l reaches the reservoir pool. to k=n and the water years range from j = 1 to j = m. x is the exponent of the expression for the distribution of suspended sediment. DA is the distance along the reservoir centerline from the point of inflow to the point The relation between simulated deposition and where no sediment remains to be deposited. HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 N37 INTERPRETATION OF SIMULATION RESULTS In table 22 DA. is an approximation of the average The range of the summer-to-winter concentrations distance over which sediment is deposited. For (r = 1.35-13.2) in table 22 is not unexpected for the shorter time periods DA can be considerably differ time periods and geographical area considered but ent because the distance through which sediment is may not be meaningful because varying discharge, transported is affected by the rate of inflow, the velocities, and so forth, were not considered. A volume of water in surface storage, constrictiors in comparison of differences between the summer and reservoir, and so forth. It appears from optimizing winter suspended sediment concentrations at sev DA that sediment distribution sometimes occurred eral southern Arizona locations shows that, for short throughout the reservoir, even when surface-water periods, r can vary more than that shown in table 22. storage was a great amount. The period 5 data suggest that the ratio of summer-to- Sediment inflow at San Carlos Reservoir does- not winter concentrations for the 38-year period 1929-66 appear to move far into the pooled water under low actually approached the 5:1 value discussed on page streamflow conditions, as illustrated by period 4 32. results in figure 39. Inaccuracies in the storage The variable a ranges from 0.25 to 0.55 in table 22 capacity ratings adversely affected all measure and averages 0.39, indicating that about 40 percent ments and estimates of sediment deposition. ^ Iso, of the total sediment was deposited near the entry of sediment distribution based on mean cross-sectional the San Carlos and Gila Rivers into the reservoir velocities or daily streamflow volume rather thar the pool. This 40 percent probably is the approximate mean distance, DA, may improve the sediment bed material discharge of the San Carlos and Gila model. These indications emphasize the need for Rivers. more development of the sediment distribution It was assumed prior to determining an optimum model. x, that x would be equal to, or greater than, 1.0; that Figure 40A shows a comparison between the vol is, the rate of suspended sediment deposition would umes of deposits measured and computed during be at least as great at the point of inflow as in any period 5 for all incremental reservoirs. In figure 405 other part of the reservoir. The selection of the a comparison is made between cumulative volumes optimum x did not confirm this assumption for all of measured and computed sediment deposits for periods. The values of x determine the curvature of period 5. The summations were determined by pro the relations in figure 39. These relations show the gressively adding the volume of deposit in an incre proportional distributions of sediment deposits mental reservoir to the sum of the deposits in all along the reservoir using the optimum values of a, lower incremental reservoirs. DA, and x determined by the simulation procedure. PROCEDURE TO DEVELOP RATINGS Reservoir surface-water storage values for the DISTANCE DOWNSTREAM FROM POINT OF water budget of water years 1929, 1935, 1937, 1947, INFLOW, IN THOUSANDS OF METERS and 1966 were obtained from surface-water capacity ratings of the five surveys. Ratings for water years 1967 through 1971 were interpolated on the basis of estimated volumes of sediment deposited from the simulation procedure by using the parameter values of period 5. For all other years, surface-water storage ratings were developed by interpolating storage changes between capacity surveys. The development of a rating of surface-water storage for each water year was begun by inserting the optimum parameter values of table 22 into the simulation procedure. Estimates of absolute sedi ment volumes, Se^, were obtained for all incremental reservoirs during the periods between surveys. rr|he ratio of the measured to estimated volumes, DISTANCE DOWNSTREAM FROM SMk/Sefc, was computed for each incremental reser POINT OF INFLOW, IN FEET voir of each period. Table 23 lists the FIGURE 39. Simulated sediment deposition, in percent, downstream from point of inflow. values for period 3. N38 GILA RIVER PHREATOPHYTE PROJECT MEASURED VOLUME OF SEDIMENT TABLE 23. Volumes of sediment deposits measured (Sj^,) and DEPOSITED, IN CUBIC computed (Se ) for 1937-47, and the SM k /Sek ratios HECTOMETERS 012345678910 24 25 Elevation S"/S" increment u £. \ i I I I i 1 i" n ' 7\ LJ (ft) (acre-ft) (acre-ft) LU LU H / I 25 H - below 2380 5,162 5,160 1.00 20 / \ O / r 24 O 2380-2385 2,411 718 3.36 a. i_ Q. 2385-2390 2,139 780 2.74 / ^i- LU[U 1*11 *7~S^ lil 2390-2395 ...... 1,926 2,189 .88 D LU D I-H- /' 1- W 2395-2400 1,312 861 1.52 - 10 2400-2405 ...... 881 740 1.19 ZLU Z Ml 2405-2410 ...... 976 695 1.40 LU (T - 9 UJ |_ 2410-2415 ...... 703 854 .82 lo 7 _ / ^ LU 5< */ - 8 D 2 2415-2420 ...... 430 428 1.01 LU LU x LU O 2420-2425 ...... 300 1,042 .29 W O 6 ' - 7 w H 2425-2430 ... . 128 1,586 .0!? / LU tf) 2430-2435 .... \ LL 168 661 .25 OD 5 - / °i 2435-2440 ...... 590 594 .99 LU ^ T 6 2440-2445 ...... 795 572 1.39 / - 5 1^ 2445-2450 ...... 189 462 .41 D W 4 - / - 2450-2455 ...... 809 515 1.57 _J O '/ ' - 4 2455-2460 ...... 403 714 .56 - - 0" 3 >z 430 439 .98 - 3 D~ 2465-2470 ...... 469 418 1.12 2470-2475 ...... 107 321 .33 pLU 2 / UJ I- Y * - 2 1- 2475-2480 ...... 304 298 1.02 rf* w A - 175 760 .23 5 1 -*/ - 1 I Above 2485 - ...... 0 0 I- / H I i i w 0 \ , i \ n LU 0 1 2345 6 7 8 ' 20 21 LU MEASURED VOLUME OF SEDIMENT DEPOSITED, IN THOUSANDS nated Sefc j. Completion of these estimates concluded OF ACRE-FEET the simulation procedure, but much of the interpola- MEASURED CUMULATIVE VOLUME OF tive computations remained to be done. The esti SEDIMENT DEPOSITED, IN CUBIC mates were multiplied by the appropriate incre HECTOMETERS mental reservoir ratio, SMk/Sefr This adjustment was required so that the interpolated storage change from sediment deposition over a period equaled the measured sediment deposition. The symbol Z dis tinguishes an interpolated volume from the esti mated volume, Se. Therefore, the volume for any incremental reservoir is (18) The annual ZkJ quantities listed in table 24 for a part of period 3 are the estimated losses in surface- water storage through interpolation from the begin ning of the period in 1937 to the start of the year shown. Subtraction of ZkJ for an incremental reser voir from the surface-water capacity at the si art of MEASURED CUMULATIVE VOLUME OF SEDIMENT DEPOSITED, IN THOU the period gives an adjusted capacity. Adjusted SANDS OF ACRE-FEET surface-water storage capacities for each year were FIGURE 40. A, Comparison between the volumes of deposits then assembled into an elevation-capacity rating for measured and estimated for each incremental reservoir, the year. The elevation and corresponding adjusted 1929-66. B, Comparison between volumes of estimated and capacity values are shown in table 25 for water years measured deposits cumulative by 5-ft-elevation increments 1938-42. upward from lowest part of reservoir, 1929-66 water years. A comparison was made between a computer- developed rating and a rating developed by curve The sediment volume accumulated in each incre fitting to determine whether computer-developed mental reservoir was also estimated in the simula ratings were acceptable for the investigation. tion from the beginning of a period to each subse Surface-water storage capacities for 1966 from table quent year in the period. These volumes are desig 1 by 5-foot-elevation increments were used ir both HYDROLOGIC HISTORY OF SAN CARLOS RESERVOIR, ARIZONA, 1929-71 I T39 TABLE 24. Estimated change in surface-water storage capacity, TABLE 26. Comparison of segments of surface-water storage Z, from start of period 3 to 1942, by 5-ft-elevation increments capacity ratings made by curve fitting and by computer Estimated loss in surface-water storage capacity, Z, in acre-ft Surface-water storage capacity, in acre-ft Difference Elevation Water year Elevation between rat-rigs, (ft) Developed by Computer acre-ft (ft) 1938 1939 1940 1941 1942 curve fitting developed Below 2380 ...... 680 1,142 1,663 2,570 3,705 2410.0 ...... 33,308 33,308 0 2380-2385 ...... 210 360 636 1,008 1,688 .1 ...... 33,563 33,589 26 2385-2390 ...... 93 173 504 1,291 1,699 .2 ...... 33,819 33,869 50 2390-2395 ...... 133 363 575 864 1,291 .3 ...... 34,076 34,150 74 2395-2400 ...... 93 141 327 542 850 .4 ...... 34,334 34,431 97 2400-2405 ...... 88 124 146 243 547 .5 ...... 34,593 34,711 118 2405-2410 ...... 118 239 239 369 613 .6 ...... 34,854 34,992 138 2410-2415 ...... 113 233 233 233 440 .7 ...... 35,116 35,273 157 2415-2420 ...... 98 184 184 184 312 .8 ...... 35,379 35,554 175 2420-2425 ...... 47 53 53 53 114 .9 ...... 35,643 35,834 191 2425-2430 ...... 20 20 20 20 70 2430-2435 ...... 28 28 28 28 112 .1 ...... 36,175 36,396 221 2435-2440 ...... 171 171 171 171 445 .2 ...... 36,443 36,676 233 2440-2445 ...... 208 208 208 208 588 .3 ...... 36,712 36,957 245 2445-2450 ...... 66 66 66 66 153 .4 ...... 36,982 37,238 256 2450-2455 ...... 222 222 222 222 555 .5 ...... 37,253 37,518 265 2455-2460 ...... 0 0 0 0 216 .6 ...... 37,526 37,799 273 2460-2465 ...... 0 0 0 0 228 .7 ...... 37,800 38,080 280 2465-2470 ...... 0 0 0 0 329 .8 ...... 38,075 38,361 286 2470-2475 ...... 0 0 0 0 67 .9 ...... 38,351 38,641 290 2475-2480 ...... 0 0 0 0 237 2412.0 ...... 38,628 38,922 294 2480-2485 ...... 0 0 0 0 73 .1 ...... 38,906 39,203 297 Above 2485 ...... 0 0 0 0 0 .2 ...... 39,185 39,483 298 .3 ...... 39,465 39,764 299 .4 ...... 39,746 40,045 299 TABLE 25. Computed capacity ratings of surface-water storage .5 ...... 40,028 40,325 297 used for 1938 through 1942 .6 ...... 40,310 40,606 296 .7 ...... 40,593 40,887 294 .8 ...... 40,877 41,168 291 FWatinn Cumulative surface-water storage capacity in acre-ft by water year .9 ...... 41,162 41,448 286 2413.0 ...... 41,448 41,729 281 (ft) 1938 1939 1940 1941 1942 .1 ...... 41,734 42,010 276 2380 ...... 6,759 6,297 5,776 4,869 3,734 .2 ...... 42,021 42,290 269 2385 ...... 12,253 11,641 10,844 9,565 7,750 .3 ...... 42,309 42,571 262 OQQrt 1 Q 9Q1 1 ft ^QQ 1 1 A \ 1 1 ^ QX^ 1 Q 1 99 .4 ...... 42,598 42,852 254 2395 ...... 27,602 26,680 25,340 22,985 20,335 .5 ...... 42,888 43,132 244 .6 ...... 43,179 43,413 234 2405 ...... 49,835 48,829 47,281 44,614 41,352 .7 ...... 43,471 43,694 223 2410 ...... 64,168 63,041 61,493 58,696 55,190 .8 ...... 43,764 43,975 211 .9 ...... 44,058 44,255 197 OXOrt QQ 9£\1 Qfi Q1 Q Q£» Q'Trt QO E\TZ QQ 7Q9 2414.0 ...... 44,353 44,536 183 2425 ...... 118,813 117,474 115,926 113,129 109,227 .1 ...... 44,648 44,817 169 2430 ...... 142,624 141,285 139,737 136,940 132,988 .2 ...... 44,944 45,097 153 2435 ...... 169,414 168,075 166,527 163,730 159,694 .3 ...... 45,241 45,378 137 2440 ...... 199,089 197,750 196,202 193,405 189,095 .4 ...... 45,539 45,659 120 2445 ...... 231,850 230,511 228,963 226,166 221,476 .5 ...... 45,838 45,939 101 2450 ...... 267,841 266,502 264,954 262,157 257,380 .6 ...... 46,137 46,220 83 2455 ...... 306,799 305,460 303,912 301,115 296,005 .7 ...... 46,437 46,501 64 2460 ...... 349,359 348,020 346,472 343,675 338,349 .8 ...... 46,738 46,782 44 (JACK QQft ft7l QQ/1 7Q9 QQQ 1 AA 3CU1 QSf7 QQ>1 QQQ .9 ...... 47,040 47,062 22 2470 ...... 446,872 445,533 443,985 441,188 435,305 2415.0 ...... 47,343 47,343 0 2475 ...... 501,110 499,771 498,223 495,426 489,476 2480 ...... 558,819 557,480 555,932 553,135 546,948 2485 ...... 620,285 618,947 617,398 614,601 608,341 2490 ...... 685,785 684,446 682,898 680,101 673,841 2495 ...... 755,274 754,035 752,487 749,690 743,430 2500 ...... 829,288 827,949 826,401 823,604 817,344 differences between ratings was 0.23 percent. F *om 2505 ...... 907,695 906,356 904,808 902,911 895,751 2510 ...... 990,544 989,205 987,657 984,860 978,600 these comparisons it was concluded that use of either 2511 ...... 1,007,672 1,006,333 1,004,785 1,001,988 995,728 2515 ...... 1,078,079 1,076,740 1,075,192 1,072,395 1,066,135 rating was acceptable. SUMMARY AND CONCLUSIONS ratings. Attention was given to the rate of change in Existing records of the hydrology of many reser capacity with respect to 0.1-ft (0.03 m)-elevation voirs can be used to make an inexpensive evaluation changes in the curve-fitted rating. The computer of reservoir performance. The records may provide rating was developed to 0.1-ft (0.03 m)-elevation sufficient data to estimate available water in bank intervals by use of a constant elevation-capacity storage and to determine water losses by evapora ratio over each 5-foot-elevation increment. A sample tion and transpiration within the reservoir bound of these ratings is given in table 26. The largest ary. It is frequently possible to investigate changes volumetric difference between ratings was 763 acre- in storage capacity and in the volume of sediment ft (0.94 hm3) at 2,462.5 ft (751 m) elevation, which deposition by use of existing capacity-survey ir for is 0.063 percent of the total surface-water storage mation. capacity. The mean deviation of the 0.1 ft (0.03 m) At San Carlos Reservoir, the water loss by evapo- N40 GILA RIVER PHREATOPHYTE PROJECT transpiration (ET) was greatest during and soon tigations Lake Hefner studies, technical report: U.f. Geol. after large water-level recessions when considerable Survey Prof. Paper 269, p. 71-119. Burkham, D. E., 1970, Precipitation, streamflow, and majo-floods surface areas of the reservoir were uncovered. Dur at selected sites in the Gila River drainage basin above ing these periods the potential for ET was high Coolidge Dam, Arizona: U.S. Geol. Survey Prof. Paper 655-B, because the exposed soils had a high water content. 33 p. ET computed by the reservoir water budget aver 1972, Channel changes of the Gila River in Safford Valley, aged 26,230 acre-ft (32.3 hm3) per year or 11.3 percent Arizona, 1846-1970: U.S. Geol. Survey Prof. Paper 655-G, 24 p. of the total reservoir outflow. Mean annual depth of -1976, Flow from small watersheds adjacent to the study ET from the exposed area was computed as 1.47 ft reach of the Gila River Phreatophyte Project: U.S. Geol. (0.448 m) in the water budget. When precipitation on Survey Prof. Paper 655-1, 19 p. the exposed surface of the reservoir was included, ET Culler, R. C., and others, 1970, Objectives, methods, and environ depth was 2.62 ft (0.800 m) annually. The changes in ment Gila River Phreatophyte Project, Graham County, ET caused by the increasing amount of vegetation Arizona: U.S. Geol. Survey Prof. Paper 655-A, 25 p. Davis, A. P., 1897, Irrigation near Phoenix, Arizona: U.S. Geol. during the period of record were not readily apparent Survey Water-Supply Paper 2, 98 p. from the existing San Carlos Reservoir data. Gottschalk, L. C., 1964, Reservoir sedimentation, in Chow, Ven Te, Evaporation from the water surface of the lake Handbook of applied hydrology: New York, McGr^w-Hill, averaged 24,611 acre-ft (30.3 hm3) per year and p. 17-1 to 17-34. accounted for 10.5 percent of the total outflow from Gila Water Commissioner, issued annually, Distribution of waters of the Gila River. the reservoir. During the period 1964-71 when evap Hanson, R. L., 1972, Subsurface hydraulics in the area of the Gila oration was computed by energy-budget and mass- River Phreatophyte Project, Graham County, Arizona: U.S. transfer methods, the computed pan coefficient was Geol. Survey Prof. Paper 655-F, 27 p. 0.80. Hanson, R. L., Kipple, F. P., and Culler, R. C., 1972, Changing Sediment deposition in the reservoir from 1929 to the consumptive use on the Gila River flood plain, south eastern Arizona, in Age of changing priorities for land and 1966 totaled 96,719 - cre-ft (119 hm3) and averaged water: Am. Soc. Civil Engineers, Irrigation and Drainage 2,553 acre-ft (3.1 hm3) per year. The mean volume of Div. Specialty Conf., p. 309-330. sediment deposited was 1.2 percent of streamflow for Lane, E. W., and Koelzer, V. A., 1943, A study of methods used in this 38-year period. the measurement and analysis of sediment loads in streams: Usable water in bank storage was computed by U.S. Army Corps Engineers rept. 9. Marciano, J. J., and Harbeck, G. E., Jr., 1954, Mass-transfer water budgets during winter periods when ET was studies, in Water-loss investigations Lake Hefner studies, considered minimal and changes in surface-water technical report: U.S. Geol. Survey Prof. Paper 269, p 46-70. storage were large. Usable bank storage was found National Weather Service, issued annually, Climatological data, to be about 14 percent of total usable storage at the Arizona: U. S. Dept. Commerce. elevation of maximum storage capacity. At lower Simons, W. D., and Rorabaugh, M. L, 1971, Hydrology of Hungry Horse Reservoir, northwestern Montana: U.S. Geol. Survey reservoir elevations, this percentage was even Prof. Paper 682, 66 p. greater. Ratings were developed relating usable Thorp, E. M., and Brown, C. B., 1951, Sedimentation in San Carlos bank storage to stage. Reservoir, Gila River, Arizona: Soil Conserv. Service Tech. The simulation of the sediment depositional pro Paper 91, 26 p. cess in a reservoir was developed primarily to aid in Turner, R. M., 1974, Quantitative and historical evidence of vege tative changes along the upper Gila River, Arizona: U.S. interpolating capacity changes between capacity Geol. Survey Prof. Paper 655-H, 19 p. surveys. The simulation was successful for the pur U.S. Army Corps of Engineers, 1914, San Carlos Irrigation Proj poses of this study. For applications in which the ect, Arizona: U.S. 63d Cong., 2d sess., H. Doc. 791, 168 p. primary objectives are to predict location and U.S. District Court vs. Gila Valley Irrigation District, et al., 1935, amounts of sediment deposited and to estimate com Globe Equity No. 59: Decree entered June 29, 1935. U.S. Geological Survey, issued annually, Water resources data for paction, the simulation model needs further testing Arizona Part 1, Surface water records: U.S. Geol. Survey and modification. open-file reports. REFERENCES CITED 1954, Compilation of records of surface waters of the United States through September 1950; Part 9-Colorado Rive" basin: Anderson, E. R., 1954, Energy-budget studies, in Water-loss inves U.S. Geol. Survey Water-Supply Paper 1313, 733 p. * U.S. GOVERNMENT PRINTING OFFICE: 1977 - 789-025/7^